Implement support for Polylang

[JoeHana]

Many users are using Polylang to publish their website in multiple languages. In fact is Polylang the recommended choice from WPCasa. To offer better compatibility between Polylang and WPCasa we've once made the plugin WPCasa Polylang. This was a great approach since the goal was to have such bridge extensions also for other translation plugins, like WPML. But after the last few years we can say now that most of the WPCasa Users are comfortable using Polylang (which btw has WPML Support), only a few use WPML itself or something like qTranslate.

But the main issue now is that WPCasa Polylang is actually only a bridge for WPCasa itself. Each further Addon like WPCasa Listings or WPCasa Favorites doesn't have Polylang Support included, neither within the respective plugin nor the WPCasa Polylang plugin.

Better would be to integrate Polylang support directly within the WPCasa Plugin, and also integrate Polylang support into every other WPCasa Addon Plugin (or even Theme).