* Add the small capital letters dead key

It can be added to the keyboard from the settings or into custom layouts
as `accent_small_caps`.

Add all the symbols listed on https://en.wikipedia.org/wiki/Small_caps

The code is changed to ensure that extra keys all use a consistent
location.

The gesture combination is mentioned. Preferred position are added.

Add "macro" keys that behave as if a sequence of keys is typed.

Macro can be added to custom layouts or through the "Add keys to the
keyboard option". The syntax is:

    symbol:key1,key2,..

The symbol cannot contain a : character. 'key1', 'key2', etc.. are:

  - 'String with \' escaping'
    The key will generate the specified string.
  - keyevent:123
    The key will send a keyevent.
  - The name of any special key

Some titles in the extra keys list are truncated and some information
are invisible.