Add generator plugin for Okular to support ODT, DOC, DOCX

Review Request #118541 - Created June 4, 2014 and submitted - Latest diff uploaded

Friedrich W. H. Kossebau
As I now and then try to view ODT documents directly in KDevelop... I wanted better support. Given that Calligra parts are no longer KPart-based, and writing a sublime-MVC-based plugin for KDevelop (like done with Okteta) would take some time, having a plugin for Okular (KPart) seems like a quick and generally nice solution.

Picked up some old work of slangkamp for another generator plugin for Okular which support ODT. Also added desktop files to extend support for DOC and DOCX (like done with PPT/PPTX). Could be extended for other doc formats for which there are 2odt/words filters, but first would like to see how this is accepted.

((Somehow I still think Okular should be part of Calligra, given the overlap of problem/solution space... but well :) ))

Used pattern OKULAR_GENERATOR_* to already match the pattern used in proposal in r118510.
Could view DOC and DOCX files in Okular, as well as had better ODT display (Okular's native ODT support is not that good).