Merge pull request #988 from ddurnev/master

[RJA-xxx] version 2.4.0-SNAPSHOT bump
[RJA-1323][feature]: "Latest version" radio button
Backend + UI
[RJA-2445][fix]: make UI aware of variable groups structure.
Add "default variable" property to variable group model.
Merge pull request #991 from ddurnev/RJA-1323_LATEST

[RJA-1323][feature]: "Latest version" radio button
issue #992: updated README