Revised forms in myaccount.php

This is a proposal to close #62 

Combines the separate forms in myaccount.php into a single row with character and action selects.

Demo: dev.forgee.se
Log in with demo/demo

In order to group the forms together the logic for handling POST data had to be revised but I kept the underlying logic intact.
The jQuery script to confirm character deletion is rewritten to work with the new form structure and I added a small JS that adds a table cell with a text input for new name inside the form table when the user selects 'Change name'. The table cell is removed again if a different action is selected.

It would be great if someone could look it over. I think that I have sanitized the POST data properly but the last thing I want is to introduce any security vulnerabilities.