Use full region width for file path panels

The horizontal margin would shrink the text button, reducing space to
show file paths in. For file paths, larger buttons make sense though, so
remove the margin.

Move text editor load/save options to filepath RNA

Cleanup: PEP 8

Merge branch 'master' into userpref_redesign

If anim player is not custom, gray out path option

Revert changes to RNA path of undo settings

Too many Add-ons use these settings, we shouldn't break them all after
beta release. RNA and UI structuring are a bit out-of-sync here now, but
that's an acceptable annoyance.

Also adds some slightly nicer grouping in the RNA file, and moves the
Weight Paint Range property to the View category to match the UI.

Merge branch 'master' into userpref_redesign

Avoid empty panel bl_label

And remove unused operator execution context change.

Tiny layout improvements

* Moved Anisotropic Filter setting to the Textures panel (it?s a
texture setting after all)
* Very minor change to Textures panel ordering
* Moved Text panel higher in the list - rather than being at the bottom
it?s not below the Display panel which makes more sense

Merge branch 'master' into userpref_redesign

Fix invisible scrollbars in Preferences

Need to force correct updates of action-zone alphas for dynamically
sized regions.

Fix responsive Preference layout ignoring hiDPI

Merge branch 'master' into userpref_redesign

Fix merge errors and whitespace cleanup

Fix "Show Preferences" shortcut not working

Was broken in 2.7 keymap.

Also whitespace cleanup.

Avoid panel content margins in small regions

Don't see a need for changes in the layout system here, a simple trick
like I've done here is sufficient.
Also: Some refactoring of the `PreferencePanel` class.

Another round of tweaks to new Preferences

- Removed doubled Cycles Compute Device text
- Moved header placement into menus panel
- Moved Text panel & rna to Interface
- Moved OpenGL Texture panel inside OpenGL panel
- Moved Color Picker Type to from System>Misc to Interface>Menus (eventually it'd be nice to include this option inside the color pickers themselves to make it more useful and discoverable)
- Combined all memory-related preferences (Undo + Console Scrollback + Sequencer Cache) in a Memory panel in System section (avoids needing previous Misc panel)
- Added correct greying out to Files > Auto Run Python Scripts panel
- Added flow layout to Save & Load checkboxes
- Rejiggered some of the Texture preferences to make more logical sense together
- A few other minor adjustments

Merge branch 'master' into userpref_redesign

Own left-bottom aligned region for Save Preference button

* Own region allows scrolling the navigation bar independently (Save
Preference button stays visible).
* We may want to change background color and size, but I'll leave that
for others to do.
* Region can be hidden but not scaled or scrolled.
* Bumps subversion.
* Added new execute region type which we may want to use in more places.
* Had to do some tweaks to drawing/layout code to get the dynamically
sized region to work without glitches.
* Also correct navigation bar versioning code to use full area width for
header.

Merge branch 'master' into userpref_redesign