User can specify session secret when installing

* Formerly, the session secret was hard coded in the app_install.js file. Now,
  there is an input box in Step 2 of the installation wizard to allow users
  to specify their own session secret.
* The input box uses a default value of "th3re is n0 sPo0n" for convenience
  when developing the application.

* Fixed small horizontal scrolling issue on Step 1 of the wizard
* Added Windows example paths for mysql.exe and mysqldump.exe