Remove third-party deps from repo

New location: https://sourceforge.net/projects/ttcards/files/
CMake OSX deps: Do not link to third-party deps

(nomlib satisfies all of our dependencies)
Introduce README.md for third-party dir
Use Github's Task List syntax for BUGS & TODO

* Add TODO items listed from i8degrees/ttcards@17eb7ed
Introduce LICENSE files for jsoncpp & nomlib
Update README to reflect current dev state

* Introduce “Why” & “Other Clones” header sections
* Re-word introduction
* Update building info (used nomlib’s README.md as the starting point)