Update fr_fr translations for 3.1.0

Add new translations:
- uiClearForm
- uiOn
- uiOff
- uiSnapToPixels

Update translation:
- alertMessageUpdateError
Fix fr_fr translations

Some spelling corrections.
Enhance fr_fr translations in UI Messages

Miscellaneous small fix and more standard messages for a better
understanding.
Enhance fr_fr translations in Help Messages

Miscellaneous small fixes and more standard messages for a better
understanding.
Enhance fr_fr translations in Alert Messages

Miscellaneous small fixes and more standard messages for a better
understanding.
Enhance fr_fr translations in Grid notation messages

Miscellaneous small fixes and more standard messages for a better
understanding.
Merge branch 'master' of https://github.com/damienbigot/messages into damienbigot-master

Conflicts:
	src/messages.coffee
Merge branch 'damienbigot-master'

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