Finish creating disable_free_space_check variable

* Create data manager variable for 'tw_disable_free_space'
* Make configurable through Settings
* Fix the "two presses needed to enable" issue for the checkbox on the
  backup screen
* No need to capitalize every word, but do specify precedes backup

Change-Id: Id436cef13e4ca9349618420aac03862ec4e3c35e
diff --git a/gui/theme/common/languages/en.xml b/gui/theme/common/languages/en.xml
index 2b80b25..28dbb6c 100644
--- a/gui/theme/common/languages/en.xml
+++ b/gui/theme/common/languages/en.xml
@@ -208,7 +208,7 @@
 		<string name="enc_enabled">enabled</string>
 		<string name="enable_backup_comp_chk">Enable compression</string>
 		<string name="skip_md5_backup_chk">Skip MD5 generation during backup</string>
-		<string name="disable_backup_space_chk">Disable Free Space Check</string>
+		<string name="disable_backup_space_chk" version="2">Disable free space check before backup</string>
 		<string name="refresh_sizes_btn">Refresh Sizes</string>
 		<string name="swipe_backup">Swipe to Backup</string>
 		<string name="append_date_btn">Append Date</string>