Fixed adding packages via project_browser
Support multiple independent source file buffers. Closes #14

 * Basic implementation:
    - All source files belong to an extra Gdl.Dock.
    - Currently there is no proper buffer_close signal handling (check if buffer
      is dirty -> dialog). Atm closing doesn't do anything.
    - "Interrupt" of closing a buffer is not properly implemented (tab
      position can change).
    - Not saved ("New document") view is not usable (completion and saving is
      not working)
 * Some minor improvements.
Merge branch 'multiple-buffers'

Conflicts:
	src/project.vala
Project browser: Always expand
Little GDL fix
Update README.md

Added GDL to deps
Set default windowed size. Gdl tabs work properly with >= 3.6.
Merge branch 'multiple-buffers'

Conflicts:
	src/ui_main.vala
Update Readme. gdl recommendation and libvala-0.16 hint.
cmake: Support custom library paths (options) from pkgconfig.

 * This will support all non-trivial library flags. E.g.
    $ pkg-config --libs mylib
    -L/usr/local/lib -lmylib
cmake: Remove debug output.
Add join_paths method to join paths together.
Switch to gee-0.8 and use custom struct for vieworder (no HashMap).
Handle source file focus detection completely with MainWindow.

 * Completion provider will crash the app.
 * Newly opened tabs aren't automatically selected.
 * New tabs aren't opened right beside the previous selected tab.
Fix vapi paths in project browser.

 * Thanks to august0815 for reporting!
Don't overwrite files with false content. Closes #25

 * Dirty hack but with ViewMap in 8fe440b55f4a323d85514837f0499829b2b35e74
   this can be done the smart way.
 * App might crash. Workarround: Disable completion provider.
Merge branch 'master' into multiple-buffers

Conflicts:
	src/main.vala
	src/project.vala
Proper implementation of method for all opened views (delegate).
Switch back to gee-1.0.

 * Switch back because Debian currently hasn't gee-0.8 in repository.
   See #695982
 * Project is still and will be compatible to gee-0.8 .
Code cleanup (pushed for LSenf).