libshell: Relocated to same level with libdeng1 and libdeng2

The "tools" source folder is optional, and libshell is required by
doomsday-server. Therefore, it cannot be under "tools".
Shell|Fixed: Added missing header
GCC|Clang: Ignore warnings about unused results in texc and md2tool
Windows: Updated VS deploy script to include libshell
Fixed: Several compiler warnings suppressed/fixed

There is a lot of thinkfunc_t related implicit casting from one
type of pointer to another. Eventually we need a safer solution for
this...
Shell: Mapping more key codes to Qt keys