Text: reworked TextRenderer internals.

 * Common layouting code in separate non-templated class.
 * Direct creation of interleaved vertex array and compressed index
   buffer, saves some memory operations and removes MeshTools dependency.
 * Preparation for mutable TextRenderer implementation.
Properly check (and document) dependencies for Text library.
Math: added vector/scalar abs() function.
SceneGraph: restarting animation should allow the same repeat count.

Updated test to check that.