shell: selective way of copying host name input

Will only copy first 64 characters of pretty host name to real host
name. This is done to avoid throwing a character limit error. Also
changes the way we call our update method when typing in the host names.
Now updates on input rather than on keyup.

Fixes #1035
shell: disables change button when necessary

When there is no input in either change host name input boxes the change
button becomes disabled.

Fixes #1036