Moved the framebuffer population to the monitor

This commit moves the populate_framebuffers to the monitor internals.
This was planned from the start and thus the code did not really change and
only the return values had to be changed.
Add string.c to CMakeLists.txt
Add ws_string interface

Add definitions for string.h
Add ws_string method stubs
Add implementation for ws_string_init()
Add implementation for ws_string_new()
Add implementation for ws_string_len()
Add implementation of ws_string_cat
Add implementation of ws_string_multicat
Add implementation of ws_string_dupl
Add implementation of ws_string_cmp()
Add implementation of ws_string_ncmp()
Add implementation of ws_string_substr()
Add implementation of ws_string_raw()
Add files for wayland buffer type
Add basic initialisation methods
Add internal buffer
Add method for querying the buffer
Merge pull request #136 from TheNeikos/move-framebuffer_init_to_monitor

Moved the framebuffer population to the monitor
Add search in base classes for ws_buffers