fixes to the installation instructions

changes to the docs/dev/environment.rst file:

• instructions should tell you to run "sudo apt-get install python-virtualenv"
• for consistency, use "sudo apt-get" rather than "apt-get"
• /path/to/new/environment is confusing. how about change this to ~/dev/virtenv with a note that says (or whatever directory you want).
• --site-packages is not supported in virtualenv, it should be --system-site-packages (maybe this has changed?)
• the instructions should tell you to run make resources, otherwise you get an error that local_rc doesn't exist
• this needs to be added for make resources to work apt-get install pyside-tools # for pyside-rcc command
• i am not sure, but i think you also need to run "make translations" (and for this you need "sudo apt-get install qt4-default", which is a bit unfortunate since this installs a ton of extra packages. maybe there is a more targetted package we could install?)
• at the end, the instructions should tell you that bitmask is installed in ~/dev/virtenv/bin/bitmask and should be in your path so long as you sourced dev/virtenv/bin/activate
• the instructions should tell you to run with --debug if it doesn't start

(from redmine: created on 2013-10-20, closed on 2014-04-09, relates #4221 (closed), relates #4222 (closed), relates #4399 (closed), relates #5300 (closed))