Moved ycmd-related files to third_party/ycmd

This is in preparation of splitting ycmd into a separate project.
Updating code to work with new ycmd location
Moving cpp code to ycmd folder
Updated CMakeLists to place libs in ycmd folder
Error message for old location libs
Shell scripts now use new ycmd location
build/test scripts split into ycmd/ycm versions
Moving ycmd deps to ycmd/third_party
More fixes for separate ycmd
Now importing ycmd's third_party folders as well
ycm tests now add ycmd/third_party to PYTHONPATH
Updating Install Guide
install.sh now removes old ycm libs if present
Fixing bug in YCM library detection
Clarified the 'old libs found' error message
Using -f with rm to get exit 0 if missing file

As per comments on https://github.com/Valloric/YouCompleteMe/commit/6572635c67df24d8f4955d10ffe9bdede2f84bc1
Support test compilation in Cygwin

Building generates warnings-as-errors from unused-local-typedefs when building the tests. Pass -Wno-unused-local-typedefs to disable this warnings.
The test executable won't link in Cygwin unless the references it needs are explicitly exported.
ExtractIdentifiersFromTagsFileWork test fails because the absolute path will be in Windows form. Skip it.
Making ycm_core_tests only compiles .dll.a and we need the .dll as well. Make ycm_support_lib as well to create the DLLs.
Cygwin executables look in the PATH for DLLs (since they are considered executables). Add YCM's python directory to PATH in the run test call.