opie-multikey: Rename buttons to add/remove custom keymap to be more clear.

opie-multikey: Rename buttons to add/remove custom keymap to be more clear.
* opie-multikey needs usability improvements at all - it may take a user
some effort to figure out that to change language layout, one needs to call
config (which lives on a key marked as shift), select language, and tap
OK at window top. Most people would tap "Add" and present with file selection
dialog with unknown to them purpose. So, name buttons "Add custom..." and
"Remove custom", to correspond to their function.