Feature/r2.5.1 renumbering

Replace all hard-coded references to version numbers with (as far as we can) dynamically-generated ones.
Sphinx is limited in what in can do in that regard; what we can do is create a styled version string ('italic-version') and use that along with text flagging the substitution. The ideal would be a Sphinx pre-processor, that did specific substitutions globally prior to processing the rst files. 
The PR also fixes the retrieval of the current version from the pom.xml.