[Flare Plugin] Fix coordinate format for import and export

Flare expects object coordinates to be in tiles instead of pixels.
Conversions have been added for Orthogonal and Isometric maps (the
2 that Flare supports).

The export function now writes the orientation of the map. This isn't
used by the Flare engine itself, but it is used when importing Flare
maps into Tiled.
Fixed Select All action to work for object layers

Now when an object layer is selected, it selects all objects on that
layer. Also it no longer does a tile selection when an image layer is
selected.

Closes #214
Split up 'Export' action from 'Export As...'

Now, the default Export action will re-export with the same file and
format used last time, without confirming the overwrite. When used for
the first time it will behave exactly like 'Export As...'.

Closes #189
Merge branch '0.10'