Pagination / Pager code review and better customizing (second try)

Reviewed Pagination and Pager.

For Pagination:

* use mixin ".pagination-size" also for base size
* make pagination variables naming scheme conform, deprecated old ones
* make pagination more customizable by supporting variables for color, bg and border in all states (default, hover, active, disabled)
* harmonize handling for inner 'a' and 'span' tags

For Pager:

* make pager more customizable by using variables of pagination for color, bg and border in all states (default, hover, active, disabled)
* deprecated variable '@pager-disabled-color', because it is now a 'duplicate' of a pagination variable '@pagination-disabled-color'
* harmonize handling for inner 'a' and 'span' tags


This is a replacement of pull request #11684