[HTML Legend] Support for nested [if] tags

[dmorissette]

Nested [if] tags are not supported in the current implementation of the HTML 
legend, but this would be required for some type of legends (requested by Peter 
B.)

This bug is about making the required changes to support nested pairs of tags in 
the HTML template parser.

[sfournier@…]

Ok, now nested if are supported. You can do something like this:
[if name=unable_checkbox value=1]	
  <input type=checkbox name=layer value=[leg_layer_name] [if name=layer_status
value=1]CHECKED[/if]>
[/if]

IMPORTANT NOTE: Metadata value "unable_checkbox" (in previous example) SHOULD be
 declared in each metadata layers.

[sfournier@…]

Please read "ENABLE_CHECKBOX" and not "UNABLE_CHECKBOX" :)

Please Jeff, update documentation... Thanks

[sfournier@…]

Please Jeff, update documentation... Thanks

[dmorissette]

Jeff, can you please confirm that documentation has been updated and close the 
bug?

[jmckenna@…]

I have updated the docs to note that nested if's are supported, and I've tested 
this somewhat.  Closing bug.