Enhance plugin metadata in MANIFEST.MF

[Hiroshi Miura(Tokyo Northside)]

Current plugin has a MANIFEST.MF that defines Plugin-Description but put URL.

It is better to set Plugin-Link for the project URL and Plugin-Description hold plain description.
Also it is better to has Plugin-Category.

Related: Feature request for OmegaT https://sourceforge.net/p/omegat/feature-requests/1549/
Related: Draft implementation of OmegaT Plugin manager https://github.com/omegat-org/omegat/pull/69

Please see a patch attached.

[ysavourel]

Implemented for upcoming version 1.8-1.41.0

[ysavourel]

Implemented manifest update. Resolves issue #27.

→ <<cset 7ab8d47b8744>>