Separate button to sync the GroupShare TMs in LanguageResources panel

When a user opens the languageResources panel, GroupShare is queried for all available TMs.

This query happens every time someone loads or reloads the panel, except if it has been done already in the last minute.

Since Groupshare is very slow with the answer in case of many existing TMs, Remy proposed to change this behaviour:

We would not load/reload the TMs from GroupShare automatically, but instead introduce a button "Synch GroupShare TMs", which the GroupShare Plugin of translate5 places in the GUI of the languageResources panel.