[FEATURE] Insert space after some symbols

[Captainbleu]

Description of the Problem

Discussed in #337
Greater/less than/equal, to, ln, log, trig... symbols automatically default to a subscript for the following number

Description of the Solution

Update src/default_snippets.js
{trigger: "\\\\(${MORE_SYMBOLS}|${SYMBOL})(.)", replacement: "\\[[0]] [[1]]", options: "rmA"}
add mid, lt, gt, le, ge and trigs fonctions to src/default_snippet_variables.js