Abstract Installer for Agasti to be Version Agnostic

The Sahana Agasti Mayon Installer is well advanced in it's implementation, level of abstraction, loose decoupling from the framework(symfony 1.4) and the cases it checks for. It is comforting to the user to have an installation that is straightforward, Sahana Agasti Mayon's installer provides this. When switching between versions of an application, or upgrading, it is important for the confidence of system administrators(or those charged with installing the application) to have consistent branding. To that degree the Sahana Agasti Mayon Installer should be abstracted to a level where the same 'installer framework' could be used in either application. This decoupling also aids in further endeavours of more easily making changes (adding components/steps to the installer)