Add functions to create text annotations (tag, comment, xml)

The common logic of these functions should be performed in the generic
writeTextAnnotation function. All the other files are acting as shortcuts to
this core function with various annotation types.
Fix inputs of writeTexteAnnotation
Merge pull request #1332 from sbesson/rebased/develop/matlab_writetextannotation

OMERO.matlab: write text annotation functions (rebased onto develop)