Plugin system rewrite

[eduardocereto]

Problems with the current Plugin System:

• Dependent on GAS, hard to port out of GAS.
• All plugins use the same namespace.
• All plugins in the end go to gas.js, so as we add more plugins GAS gets bigger, even if you don't want to use these plugins.
• We should be able to select only the plugins we want
• Possibly load plugins on demand. May be overkill since current plugins are not that large.

[brodseba]

Maybe, you could use something like Bootstrap do. You have a web interface to choose the plugins you want. The system then only "append" the plugins needed to the gas.js file for download. Not a perfect solution, but still a nice work around.