Changes for generation of Invoice
VAT-388 Added new files for generation of invoice.
Removed same code from postprocess() function which is required for Invoice generation and PDF generation
Changed hard coded URL for image and changed variable  to .
VAT-388 some minor changes for code
VAT-388 Added message templates of contribution invoice receipt for handle upgrade
Removing line used to get configuration array
Some minor changes for Invoice.php
Revert "Removing line used to get configuration array"

This reverts commit eb12c6d02725226412951ae9c64366e3367a26ee.
Merge pull request #7 from rohankatkar/VAT_Issue_388

VAT-388  Added action for Print or Email Invoice. Created template for invoice.