Stylization: Adding support for text justification

[louisewatson]

The justification text attribute was not implemented for either plain text or mtext.

[louisewatson]

This submission adds code to the font engine to process justification settings.

Small changes were made to RS_FontEngine for the plain text case. Text alignment adjustments are made for justification and then horizontal alignment is used to position the entire text block.

A bit of RichTextEngine? was reworked to support justification. Here the code needed to consider that the text might contain local justification changes; eg. stack fractions (\S). This required a change to the way the text run data is stored. Now the code organizes the data in blocks. Blocks consist of lines which may themselves contain other blocks.

Finally, while in the font engine, a problem with the \S mtext op-code was fixed. Now a code in the form of "\Sa^{;" works. That is, a stack fraction without a denominator evaluates correctly.}

[waltweltonlair]

Louise fixed this with submission  https://trac.osgeo.org/mapguide/changeset/3109.

[waltweltonlair]

Merged fix into branch stream with submission  https://trac.osgeo.org/mapguide/changeset/3134.