use Python 2.7 only
added a lock to tts.py (just in case) ; now locks are used in a "with" statement

(cherry picked from commit cfde58255ccd6ebebab34142120b4c14eed60d6b)
(cherry picked from commit 2871d97b1024ef70836d1c22a4ac0cd1b7aa1300)
(cherry picked from commit 0d924abfa8e2e5120805e03625b777db7dac0c2c)
(cherry picked from commit b0a315842e3597cf4aed50c6e4bdaae232458008)
(cherry picked from commit be6c769254294dc3e0baae0875a4560d297b1e70)
added to input_string() a feedback when the string is validated

fixes #5

(cherry picked from commit 6adfb9da6a8e937adf695e56cca067a35f557a68)
chat messages won't be spelled anymore during editing

(cherry picked from commit 898cbdceed5bec0c901f5e9c784b065fda4c3470)