Use EIP-712 signedTypedData in Web3's HttpProvider as signer

This PR is the first approach to the future transaction in smart contracts used by this application.

The logic has been wrapped into a feature flag where PersonalEdition contracts were used to handling a transaction, signing it using the signedTypedData function from EIP-712.

The provider used by this proof of concept was the general Web3's HttpProvider.

Integration of transaction-history-service V1

Description
This PR introduces the transaction-history service mechanism of recomposing txs previously created. For achieving that we interact with backend service, sending information after each txs and then, fetching txs based on a given safe.

You can take a look into the backend service: safe-transaction-history service

Select, add, remove and transfer custom ERC20 Tokens

This release includes the next major features:

• Select enabling or disabling which tokens should be shown in the safe view
• Adds and removes custom ERC20 tokens
• Allow transfer tokens

Also, it includes the next major bugfixes and features:

• Only fetches funds of enabled safe's tokens
• Mocked fetchBalances endpoint in JEST tets for retrieving the default tokens in a faster and more controlled way
• Disable "NEXT" button in multi-step forms when validation takes time (i.e when checking if the token has human readable information)
• Improved the Suite test speed in 50%+
• Usage of gnosis/utils-contracts project for general token contracts.
• Simplified the UI (now ETH transfers are managed in the safe's balance section)

Remove owners & Edit Daily Limit

This PR includes the logic for removing owners and editing daily limit

Some technical aspects:

• Started a parallel WIP test mechanism for improving its speed
• Fixed bug found where the app did not wait until transactions were mined
• Included Snack Bar component for advising notes to the final user
• Bunch of fixes and code improvements

Change threshold & Add Owners

WA-234 & WA-235, in this release the next logic is included:

• The option to modify the threshold of a safe
• Adding owners functionality (including the option to modify the threshold)
• Pull mechanism for detecting changes on displayed safe (storing owner's names independently and also fetching data of safe to Ethereum node directly)

Withdrawn functionality

This PR includes the logic for being able to operate Withdrawn operations on the safe.

Some technical aspects:

• Features covered by DOM tests
• Visualization of components are covered by storybook tests
• Internal logic management is done under not optimistic way relying on mocked service taking advantage of super optimized immutable-reselect libraries for updating UI
• Transactions use a gas station and also precalculated of units of gas needed for each transaction
• It uses the latest version (at this time) of the safe-contracts

Display and auto-update safe's funds

Merge pull request #16 from gnosis/feature/WA-230-display-eth-funds

WA-230 Display and update ETH funds

Create Safe

This release includes a major feature implementation: "Create Safes" also includes a bunch of fixes, tests for assuring the process is correct, and a set of general classes and functions for future development.

Safe React - Project stable

This tag enables a basic usage of the project. It contains an updated DevOps configuration and put the project in the right scope to start developing.

In this PR we include:

• Babel 7 and Webpack 4 configuration
• Flow, EsLint config
• Travis and surge automatic deployment when developing
• README and LICENSE project information
• Frontend libraries like Material UI Next