Analyzer plugin framework

[vladak]

As discussed on Slack #dev channel, some (namely @tarzanek) would like to add some new analyzers (e.g. PDF analyzer - #492) written in Scala/Kotlin/Closure/you-name-it. Given that core OpenGrok should stay pure Java, we need a plugin framework and interface for the analyzers to facilitate this.

The repositories for analyzers can be then hosted anywhere (our own would live under https://github.com/OpenGrok/) and the jars published to Maven central. This should also allow for 3rd party analyzers - just shove them under analyzer directory (configurable) and OpenGrok will load them automatically.

[tulinkry]

We can somehow reuse the existing framework for authorization plugins.

[vladak]

Yeah, that would be nice.

[vladak]

Some things for consideration:

• analyzer should be able to add items to the 'File type' drop down menu in the UI
• should be possible to add options to ctags