Part 2:  new methods in PluginBase.

+Continuing implementation of new methods for PluginBase class:
PluginBase.OnClose(). Added calling when close button is pressed.
+New file "PluginVersion.cs" with class VersionAttribute. Prospect class
to detect version of methods in runtime. - experimental -
+Corrected some warnings in GEAR code, for compiling in MONO. Some more
left...
+Corrected "compileMONO.Bat" to clear unnecesaries directives (changed
by "-pkg:dotnet" option). Simplified to run under MONO Command Prompt,
not normal CMD.