standardize plugins, update metadata

add about-plugin metadata
chmod -x plugins
cleanup filenames to standardize on x.plugin.bash format
only plugin files intended to be executable from the command line should
contain a shebang line, and should be a+x.

plugins/available/latex.plugin.bash

@@ -1,4 +1,5 @@
-#!/usr/bin/env bash
+cite about-plugin
+about-plugin use mactex
 
 # add mactex to the path if its present
 MACTEX_PATH=/usr/local/texlive/2009/bin/universal-darwin