added validation checks on the back end of the name input value as well ...

...as for the network value in case a user has no-script turned on and therefore bypasses the front-end checks.

This pull request addresses issue https://github.com/opentechinstitute/luci-commotion/issues/144

To test. 
1) On an existing node try to use the following formats for a mesh name with noscript turned off and then again with it turned on.
 * 0 chars 
 * more than 15 chars
 * a name containing the following chars $\"[]?+/
 * a name starting with a space, !, or # char.

If it ever sets an incorrect name reject this pull request and I will fix it. Otherwise MERGE ME!