Remove signal.SIGINT handler from simple CLI

At some point during refactoring the ability to hit Ctrl+C to exit the basic CLI was lost.

The signal.SIGINT handler is needed by the graphical GUI, but it
interfered with the use of sys.stdin.readline() in the simple CLI.
Rearrange the installation of the handler for only the GUI.

To test, run:
   mycroft-cli-client --simple
Then hit Ctrl+C.  Before this change nothing happens (you just see the "^C" printed out).  After the change it exits as expected.

mycroft/client/text/__main__.py

@@ -13,13 +13,15 @@
 # limitations under the License.
 #
 import sys
+import signal
 import io
 import os.path
 import curses
 from mycroft.util import get_ipc_directory
 from .text_client import (
         load_settings, save_settings, simple_cli, gui_main,
-        start_log_monitor, start_mic_monitor, connect_to_mycroft
+        start_log_monitor, start_mic_monitor, connect_to_mycroft,
+        ctrl_c_handler
     )
 from mycroft.configuration import Configuration
 
@@ -57,6 +59,8 @@ def main():
         sys.stderr = sys.__stderr__
         simple_cli()
     else:
+        # Special signal handler allows a clean shutdown of the GUI
+        signal.signal(signal.SIGINT, ctrl_c_handler)
         load_settings()
         curses.wrapper(gui_main)
         curses.endwin()

mycroft/client/text/text_client.py

@@ -14,7 +14,6 @@
 #
 import sys
 import io
-import signal
 from math import ceil
 
 from .gui_server import start_qml_gui
@@ -121,9 +120,6 @@ def ctrl_c_pressed():
         return False
 
 
-signal.signal(signal.SIGINT, ctrl_c_handler)
-
-
 ##############################################################################
 # Helper functions