Split out library to build standalone plugins for web applications

Signed-off-by: Simon Busch <morphis@gravedo.de>
Correctly use terms "plugin" and "extension"

Signed-off-by: Simon Busch <morphis@gravedo.de>
Implement support for application plugins and extensions

Signed-off-by: Simon Busch <morphis@gravedo.de>
Merge pull request #9 from webOS-ports/morphis/extensions

Add support for extensions