only override root dir for interface externals if they don't exist
more standardization for external library searches
cleanup HifiLibrarySearchHints cmake macro
more Cmake cleanup to grab externals
search only in lib for Leapmotion lib
remove a lost s
fix HAVE_QXMPP wrappings in XmppClient
remove extra wrapping HAVE_QXMPP if
change to new style of signal slot connection for XmppClient
add back the lost QXMPP_STATIC definition
Merge pull request #3212 from birarda/select-library

standardization of hints used to find external libraries