more functionality for collector objects

[ThomasBreuer]

create an Oscar collector from a GAP collector

(suggested by @fieker)

[codecov]

Codecov Report

Attention: Patch coverage is 94.59459% with 2 lines in your changes missing coverage. Please review.

Project coverage is 84.78%. Comparing base (7769ffa) to head (72450c6).
Report is 25 commits behind head on master.

Files with missing lines	Patch %	Lines
src/Groups/pcgroup.jl	94.59%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4157      +/-   ##
==========================================
+ Coverage   84.58%   84.78%   +0.19%     
==========================================
  Files         631      631              
  Lines       84829    86314    +1485     
==========================================
+ Hits        71754    73178    +1424     
- Misses      13075    13136      +61     

Files with missing lines	Coverage Δ
src/Groups/pcgroup.jl	76.10% <94.59%> (+5.36%)	⬆️

... and 28 files with indirect coverage changes

[ThomasBreuer]

restart the tests ...