WINDOWS: Check for python before creating the search engine tab. Prevents the creation of python specific files in the user's PC if no python is found. Closes #1370.

Conflicts:
	src/mainwindow.cpp
	src/searchengine/searchengine.cpp
	src/searchengine/searchengine.h
WINDOWS: Don't create keys in the registry if python isn't found. Closes #1370.

Conflicts:
	src/preferences/preferences.cpp
WINDOWS: Can now correctly detect 64bit and 32bit python installations on 64bit Windows. Closes #1148 #445 #795 #1708.

Conflicts:
	src/preferences/preferences.cpp
WINDOWS: Search first in PATH for python. Closes #956.

Conflicts:
	src/mainwindow.cpp
Don't display the Search Engine tab by default.

Conflicts:
	src/preferences/preferences.cpp