Fixed segmentation fault in stamp brush random mode

Tiled crashed when right-click dragging an empty area and then trying to
paint with Random Mode enabled.

Since no random tile could be selected, brushItem()->tileLayer() ended up
as NULL, but when painting it was used unconditionally (the mStamp was
checked, but that is no longer the tile layer used for painting).

The check whether the stamp is outside the map was corrected as well.
Update all objects in a group when changing the group color

Since recently the object color is cached in the MapObjectItem class, so
we need to emit the objectsChanged signal rather than just asking for a
repaint.

Fixes #106
Updated the Japanese translation
Updated the Spanish translation
Flare plugin: Updates and simplification
Flare plugin: Fixed bug when map width/height are not equal
Flare plugin: Small tweaks

* Set UTF-8 as codec instead of using QString::toUtf8
* Use QString::isEmpty rather than comparing to ""
Updated the Chinese translation
Updated Czech translation
Bumped version to 0.8.0 and updated NEWS file

Slowly getting ready for release.
Fixed pixel size in new map dialog for isometric maps

The displayed pixel size assumed plain orthogonal maps. Now it relies on
the appropriate map renderer to tell it the pixel size of the map.
Added alternative shortcuts to switch between documents
Fixes to the German translation
Updated the Dutch translation

Also fixed the translation of two plural-enabled texts in the German
translation.
Updated the French translation

With some corrections by Yohann Ferreira.
Updated the Brazilian Portuguese translation
Fixed some UI strings to get updated when the language is changed

The Command and Random Mode button tool tips were not picking up a
change of language.
Added support for polygon objects to the JSON plugin
Updated NEWS file again

Three more translations were updated.
Added Qt translations and qt.conf to the Windows installer

This fixes the translations of some built-in strings like those on
'OK' and 'Close' buttons, context menu of scroll bars and built-in
error messages.

The qt.conf fixes loading of shipped Qt plugins used for supporting
jpeg, gif and tiff as image formats as well as some text codecs.