merge de.ics and de-COMMON.ics,

there's no need to be overly anal about who's responsible for
which holidays.  Juridically, the holidays from (former) de-COMMON.ics
are not to be decided by the 3166-1 country de, but by its 3166-2
subdivisions.

Signed-off-by: Sebastian Freundt <hroptatyr@fresse.org>
add holidays for England, Wales, Scotland and Northern Ireland

Signed-off-by: Sebastian Freundt <hroptatyr@fresse.org>
add Queen's Jubilee and substitute Spring Bank Holiday

Signed-off-by: Sebastian Freundt <hroptatyr@fresse.org>