Fix util.is_mm_project() function

Added check for /config/.settings file, used for showing menus, etc
Implement is_visible() and is_enabled() for MavensMate commands

Programmatically enable and disable menu commands - hide when not a MM
project, disable conditionally on file type and contents.
Open on Server

Implementation of open_sfdc_url command for plugin. Conditionally
show/hide.
Clean up comments and functions

remove unused logic and correct, hide menu items based on file type and
enable based on contents.
is_mm_file() fix

syntax error
update is_mm_file()

Check fore meta.xml file of the same name to determine if it is synched
to the server.
Menu updates

Add stub command that is disabled when there are no valid commands
availabe for the view (not MM file).
Merge pull request #134 from doublesharp/open-on-sfdc

Open On Server, Menu Enhancements, Bug Fixes