T37247 - Modifier "Mask" not updated correctly when switching from objects

Fix T37485: autocomplete while appending and autocomplete folder behaviour.

This adds functionality to tab-autocomplete folders in the file browser file
field, and the ability to autocomplete .blend files and their sub folders while
linking. If only one match of a blend or a folder is found, it is opened, which
applies to wildcards in the file field now.

Reviewed By: elubie, brecht

Differential Revision: https://developer.blender.org/D20

Fix: tab completing a filepath name in file browsers asks to create a new
directory if name was not fully matched

When hitting tab to complete a directory name in the filepath field in the
filebrowser Blender shows a "create new directory?" popup, if the beginning
of directory name typed in the field matches many entries. For example if you
have directories in the open directory called "test123" and "test456", typing
"te", tab would complete up to "test", but ask to create a new folder with the
name "test".

This patch unsets the boolean storing the info about changing filepath if the
folder with the completed name does not exist.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D10

Transform: vertex snapping for curves

This adds vertex snapping capabilities for curves. Snaps to all control points
of other objects, and visible + selected control points and handles in curve
edit mode.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D3