* Added support to label text alignment.
Since labels in gtk can't be aligned via css (I still don't know why)
and can be only aligned using code, this patch adds support for this
functionality by adding the properties :xalign and :yalign to the label
expression.
The exact behavior is described by the docs.
* Updated changelog with :xalign and :yalign for labels
* Add drag and drop functionality to eventbox (fixes#409)
* Don't allow dragging empty string values
* Support dragging text
* Provide the type of drag element to the command, separate out day month and year in onclick event of calendar
