Performance of main client loop up to 2x faster In places, up to 3 times faster

NOTE 1: This does not mean a 2x increase in framerate. Increase in fps may be up to 1-2fps
NOTE 2: This local 'caching' of settings is not optimal and an alternative solution will be worked on after 0.4.11 is released
Rewrite generate notification mechanism

Add support for notify-on-decoration
Clean up mapgen constructors
Clean up mapgen.cpp code style somewhat
Remove trailing whitespace from some files
Build for win32 & win64 on Travis too
Add workaround for failing clang build
Close settings files and save them correctly
Ignore some mouse events sent from scrollbar to GUITable

Fixes #1567, #1806.
Add minetest.clear_registered_biomes() api
Schematics: Fix minetest.place_schematic() when defined by a Lua table
Mapgen V5: Fix use of uninitialized value in ctor
Fix regression (increase/decrease viewing range with +/- keys)
Restore finalColorBlend implementation in shaders.