Enable the use of input format names in the <format> tag when adding blocks

When adding blocks one can specify the
. However this only supports the use for input format ids. My patch (attached) allows one to use either the input format id or its full name. The patch will validate the format data to ensure that the format is valid before the form gets built and executed.

Example:

<block>
  ...
  <format>Full HTML</format>   <!-- will get translated to the correct formate id by block.inc code -->
  ...
</block>