[SVG] Add support for font-size keywords

Bugs:

1. https://bugs.documentfoundation.org/show_bug.cgi?id=96046
2. https://bugs.documentfoundation.org/show_bug.cgi?id=97275

Commits:

1. https://cgit.freedesktop.org/libreoffice/core/commit/?id=406cdc29039e5e65bacfcd635de8022642d63547
2. https://cgit.freedesktop.org/libreoffice/core/commit/?id=288d1f802d306dc741df60c029c50850e7e5fd6b
3. https://cgit.freedesktop.org/libreoffice/core/commit/?id=805b328858e2d1414e7a9e7701c42a41ede2a617
4. https://cgit.freedesktop.org/libreoffice/core/commit/?id=5ee943a11f46abdd1c0200925a71a8dc19d8965e

Sample File: http://imgh.us/font-size.svg

Results:

Libreoffice 5.1

Libreoffice 5.2