Settings: Remove unused property

Also fix migration mapping
Settings: Fix legacy settings locator

Also fix new global settings path
to use per-user directory.

Also update ConfOxide to save formatted JSON,
Settings: Skip invalid legacy enum values
CSS: Don't crash when opening standalone CSS files

Don't use ProjectItem unnecessarily
Margin: Fix pane width serialization

Don't choke on bad values
Don't save NaN
Use original value name
Tests: Test basic LESS compilation
Tests: Expand compilation tests

Test minification & disallowed extensions

Fixes two bugs.