Fix::Auto metadata generation made optional

Previously _prepareDocument function was called for rendering a HTML
page, it automatically generate metadata for the page from menu and
global configuration. This overwrites all metadata set by component.

A new flag 'auto_generate_metadata' have been defined on html-view
(default to true). If flag is ON, framework will automatically generate
data.

The views who want to generate there own metadata can
1. Override generateMetadata() function
2. Or set falg auto_generate_metadata = false and call
Rb_HelperJoomla::addDocumentMetadata() manually

Impact : _prepareDocument() renamed to generateMetadata()

Fixes #23
Chore:: Removes PayPlans constant

Removes code refering to Payplans version.
TODO : This function should be named properly.

Refer #31