replace watchdog with active polling thread

watchdog does not work on windows. For some
reason file modification events are not
emitted.
Fixed by replacing watchdog with a thread
that polls the modification date ever 0.5s.

Also fixed a bug that the hit view was not
properly destructed.

make_installer.py

@@ -18,9 +18,7 @@ arguments = [
     '--add-binary', 'changelog.txt' + os.pathsep + '.',
     '--add-binary', 'version.txt' + os.pathsep + '.',
     '--hidden-import=krowlog',
-    '--hidden-import=watchdog',
-    '--hidden-import=watchdog.observers',
-    '--hidden-import=watchdog.version',
+    '--hidden-import=__future__',
     '--hidden-import=configparser'
 ]