Moving files and updating code to reflect the following schema:

install (was install_from_zip, also includes windows installer): getting files from scratch, calling into setup
update (update command): updating files, calling into setup
setup (was install management command, and install scripts for each OS): with files available, set up the system to run
Rebranding central server "install" to "download"
Make update command work--even if central server object doesn't exist.  Tweak updates app
Moving update command to ... updates app. Duh :)
Reorder code so that full set of install-related files can be passed to the install script.  Then, pass file list to the install script, so they can be cleaned up after install.
Be more careful about moving around files, during install.
Move videoscan into setup, call setup from update.
fixing small import bug
current_stage is 1-based, not 0-based!  And fix up semantics (and funciton!) of started() vs completed()
Merge branch '1047_1048' of github.com:bcipolli/ka-lite into 999
Adding a function to determine what port users should use, and change reporting based on install vs update
Merge branch 'release-0.11' of github.com:learningequality/ka-lite into 999

Conflicts:
	kalite/templates/central/homepage.html
Merge pull request #1084 from bcipolli/999

Make update script call into setup (which detects it should do an update)