Minor string cleanup (#248)

- Simplified some strings to not include unnecessary markup.
- Fix translator comments so that they actually make it to glabels_C.ts file
      - Reconciled the style of these comments.
      - Added translator comments

glabels/ColorPaletteDialog.cpp

@@ -265,7 +265,7 @@ namespace glabels
 				mColorNode = newColorNode;
 			
 				// TRANSLATORS
-				//: %1 = color specification in hex. String must not contain a colon (:).
+				//:   %1 = color specification in hex. String must not contain a colon (:).
 				mColorHistory->addColor( mColorNode.color(),
 				                         QString(tr("Custom Color %1")).arg(mColorNode.color().name()) );