Avoid the standard QMainWindow context menu in the collision editor

The standard context menu allows hiding the tool bar, after which it is
impossible to get it back without restarting Tiled. Now, a somewhat
useful context menu is shown instead which has the names and shortcuts
of all actions.

Closes #812
Merge branch '0.10'
Added support for flat-top hexagonal (staggering the X axis)

This also adds support for staggering the X axis at either odd or
even indexes for staggered isometric maps.
Lua plugin: Write out tile terrain information

Turns out I need this for a my current project so it must be useful.
Flare plugin: Fixed ability to open maps with absolute paths

Saving maps with absolute paths is a bad idea and is avoided whenever
possible, but it is the only way to reference files on a different
drive on Windows.

Closes #826
Update tiled_pt.ts
Merge pull request #827 from porfirioribeiro/master

Update tiled_pt.ts
Added uniqueIDs to MapObjects
Some object unique ID changes

I think it's enough to just call it the object ID, and document that
these IDs are unique for each object on the map.

Since the first valid object ID is 1, the property is initialized with 0
now instead of -1.

Removed unnecessary ID assignments from MapWriter and
VariantToMapConverter. Any objects that don't have an ID assigned yet
will get one assigned once the ObjectGroup is added to the Map.
Added an example hexagonal map

Based on public domain tiles by pixel32, found at:

http://opengameart.org/content/pixel-hex-tilesets-enhanced
Removed some unused defines
Added a CSV export plugin

This plugin only exports the first tile layer. Tiles are written out by
their index in the tileset, or by their "name" if this custom property
is set on them. Empty cells are written out as -1.

Closes #277
merged with upstream