Minor change: Make Splitter::getPosition() inlined
Add the old "Animation Editor" as a timeline at the bottom of sprite editors (Workspace)

- Renamed AnimationEditor (dialogs/aniedit.h) to Timeline
  class (app/ui/timeline.h)
- Renamed FilmEditor command to Timeline
Minor fix in TODO
Move src/app/dialogs/maskcol.cpp to src/app/commands/cmd_mask_by_color.cpp

Finally src/app/dialogs directory is gone.
Fix typo in TODO.md
Fix Mask::byColor()

Bug introduced in commit e5ba8e0922e066e7b521b149007a74aa00a9a25b
Fix main_window.xml to show the ContextBar again
Timeline: smaller row size
Timeline: we've to observe the Context to know if the Document is destroyed

In this way the timeline can stop observing the Document when it's closed.
Fix bug: Notify Context's observers in Context::onAdd/RemoveDocument
Keep timeline in sync with current editor and after commands are executed
Add SKIN_PART_NESW(name) macro in skin_parts.h
Remove thumbnails generation code

At the moment we'll keep the timeline simple (without thumbnails).
Fix bug creating bitmaps with width < 0 in draw_color() function
Add the Palette menu with Load/Save commands
Fix issue #277, LoadPalette command can change the default palette
Merge branch 'dev' of git@github.com:dacap/aseprite.git into dev
Add option in INSTALL.md to copy data/ dir to ~/.aseprite on Linux
Add CONTRIBUTING.md file
Minor changes/fixes in CONTRIBUTING.md