Write information about deps in plugins.

Write the build environment to a list section of the plugin
meta-data. This should make it easier to figure out what
on earth is going on when everything breaks.

Change-Id: I317cd6795e81d56930b21b8d9beeabc28a0b775e
Reviewed-on: http://gerrit.dmdirc.com/4010
Reviewed-by: Greg Holmes <greg@dmdirc.com>
Automatic-Compile: DMDirc Build Manager