[meta] Lara's UX improvements

See also this post (in French). Here's the actionable items:

• French translation: replace "Nouveau.elle" by "nouveau ou nouvelle" in onboarding.
• Remove the close button animation in the modale.
• French translation: replace "Opération" by "Libellé" (and Label in English) in the transaction list table header
• Split the search / sync / add new transaction button list into three separated buttons.
• Differences chart: if there are no transactions during a month, it's missing in the list of months in the legend, which can be confusing.
• Add an explanatory text for the charts by currencies, to explain there's no conversion going on.
• Remove the icon for default parameters opening modals buttons, since they're adding confusion with the global cog menu button.
• Duplicates: move the "find more / less" button to their own line
• Duplicates: add visual feedback (short notification?) when the thresholds have been changed.
• Categories: add visual feedback when default categories have been created.
• Categories: add the number of uses next to each category, in the table.
• Access mgmt: use a sync icon to resync an account's balance. (there already is a sync icon for accounts refresh, disabled for now, see !1073 (comment 527317))
• Administration: tweak the message related to the sync setting

If you're interested to fix one of these items, please let us know, and/or feel free to open an issue to discuss details, if needed.