Update michagogo's gitian pgp key, adding UIDs
Reimplement CBlockLocator's chain-related logic in CChain.

This removes a few unused CBlockLocator methods, and moves the
construction and fork-finding logic to CChain (which can do these
more efficiently, as it has a height-indexable chain available).
It also makes CBlockLocator independent from the validation code.
Move CBlockLocator to core.h

As CBlockLocator is a P2P data structure, and independent from the
validation logic, it can be moved to core.
doc: remove readme-qt.md

Now that autotools is used as a build system there is nothing
special about building the GUI anymore. Merge the salvageable
parts into build-unix.md
doc: build with qt5 is currently not possible

Add as a separate commit so that it can be easily reverted once
Qt5 is supported again.
Merge pull request #3083 from sipa/chainlocator

CBlockLocator improvements & move to core
Merge pull request #3092 from laanwj/2013_10_remove_readme_qt

doc: remove readme-qt.md
Merge pull request #3086 from Michagogo/update-pgp

Update michagogo's gitian pgp key, adding UIDs