Fix a couple bugs.

Fixes 'unknown' fppMode setting when changing to player mode via the UI.

Fixes common.php's WriteSettingToFile() and ReadSettingFromFile()
dealing with commented entries in the settings file.  Previously
commented entries would have been read and updated since the regex
match wasn't looking for the setting name at the beginning of a line.
This also fixes an unseen bug where we could have setting names
colliding if one full setting name matched the end of another setting
name.