LPS-43009 Hook to support RTL feature in 6.2.x

Hey Brian,

The goal of this plugin is to support RTL features (included by default in Liferay Portal 7.0) in 6.2.x. It'll be distributed through the marketplace. First commits provide the basic feature. Then we added a tool to support RTL in theme plugins. Finally, we've applied the same bug fixes as in master.

Regards

@juliocamarero
@jbalsas