Fixed issue with Yahoo! Mail not working, fixed command-line commands not working

-Added Yahoo! Mail to list of trusted servers (hopefully also fixes TLS conversion error)
-Made program add user-specified server to list of trusted servers (does not persist across program instances)
-Fixed issue with potential NullPointerException being thrown while setting new host in Email.java
-Added "Use BETA Versions" checkbox in Preferences, disabled by default
--Currently unused
-Removed space characters from input in command-line interface (was not working)
-Changed version to 1.7.1