1.2.2 : Slightly better error messages

The previous error messages when the Expression menu is full were pretty much unreadable, so they've been rewritten.
Also the error message now comes with a new button, allowing you to quickly open and edit the Expression Menu in question, which makes the process slightly simpler.

Also, turns out that I was dead wrong on the "Reset avatar" button.
This button is always added. Even if you fill the menu with 8 controls.

So the maximum amount of controls allowed in the main menu are now :

• 7 (8-1) controls for Constraints
• 6 (8-2) for Particles.

I could make the limit 7 for Particles too by moving the two added buttons to a submenu, and adding this submenu.
I'll see if people are really hindered by this limit, since this requires additional tests, and remaking parts of the presentation videos.