LDA version number should not be hard-wired

[randykerber]

Currently, the LDA version number is hard-wired into the source code, in graphs/linkeddataapigraph.class.php.
When updating this to a new version, like from "2.1" to "2.2", the process is to search for occurrences of the string "2.1" and manually change some of them to "2.2". This is a process prone to error. It's easy to confuse the version number of an app from the version number of some included library.

The app version number should be set in one place as a configuration or global constant.