Adapt to Gerrit 2.11.3

[tomaswolf]

Gerrit 2.11.3 release is imminent; probably the week-end of Aug 21-23. The plugin will need to be adapted. Refactorings needed:

• change dependency to gerrit-api 2.11.3.
• remove direct dependencies on parboiled in Gitblit code (some isolated and completely unnecessary instances).
• check that markdown rendering still works (Gerrit 2.11.3 replaces parboiled by grappa 1.0.4). Should be compatible, but one never knows. If it doesn't work, re-include a relocated pegdown/parboiled combo in the shaded jar for use by Gitblit.
• Gerrit 2.11.3 switches to Guice 4.0; we should be able to remove the FixedGuiceHttpServletRequest.

New release of this plugin should be ready at most a few days after Gerrit 2.11.3 has been released.

[tomaswolf]

Done in release v2.11.3.162.1.