Major revision of CSS utilities

- base.xsl defines the CSS syntax and provides utilities for parsing,
  validating, inheriting, defaulting, serializing and evaluating CSS
- CSS is now parsed into elements like css:rule and css:property,
  instead of string sequences
- braille-css.xsl extends base.xsl with property definitions
- moved everything to css-core. css-utils is now just a "meta module"
dotify-saxon: use the "official" Dotify OSGi bundles

also refactored a bit and added a test
liblouis-core refactoring

- liblouis table is now represented by a list of URIs, consistently
  throughout the API
- new interface LiblouisTranslator, the Liblouis interface has become a
  provider of LiblouisTranslator
liblouis-core: add `display` to LiblouisTranslator interface
Add module liblouis-pef

Implementation of org.daisy.braille.table.TableProvider based on
liblouis display tables.
Add module liblouis-dotify

Implementation of org.daisy.dotify.api.translator.BrailleTranslatorFactoryService
based on Liblouis
Add module dotify-calabash

Provides dotify:obfl-to-pef step.
common-utils: helper steps that can be shared between formatter implementations

also improved css-core
- added properties white-space and content
- added functions for parsing string-set and counter-reset
Initial Dotify-based formatter implementation
Refactoring or CSS helper steps in common-utils

- Made steps somewhat more low-level/atomic. They now match better the
  basic CSS processing steps as explained in the specification.
- Made the steps more self-documenting: step names, elements and
  attributes are expressed as much as possible in terms of CSS concepts.
- It is now possible to deeply parse a document and obtain a
  fully-fledged intermediate representation of the document according to
  the CSS model, that is better suited for further processing by a
  renderer.
- Updated dotify-formatter accordingly.
Use Dotify through OSGi services instead of Spi Fly
dotify-calabash: translate generated numbers to braille
dotify-formatter: Support border and padding properties
dotify-calabash: translate numbers also if they are part of a string
Move css stuff from common-utils to css-utils
css-utils: step for migrating to a custom CSS definition

The new CSS definition consists of a list of properties and the 4
function is-valid, is-inherited, initial-value and applies-to, all of
which are possibly context dependent.
Make the latest versions of all modules work with each other
Update README's