Merge common stuff with WinCenterTitle

[valinet]

Hooking Explorer is done in a similar manner to hooking DWM in WinCenterTitle. That has been recently updated and polished. It is advisable to move the similar parts (hooking and parts of pdb.h) to a common library, which both these projects should reference, so that is easier to maintain them.

Or, the ugly solution, for now, backport changes in WinCenterTitle here (not advisable).

[valinet]

I made a new repository, libvalinet, that contains the common logic shared by the two applications, and will contain, in the future, general implementations of various things.