Add 'Current application version' to website footer

[florisrobbemont]

Get the current revision (MSBUILD Task?) during build and store it inside KeyHub.Web.dll. We can then display this on the site to keep track of the currently deployed version

[lilith]

I do this already with ImageResizer: https://github.com/imazen/resizer/tree/master/tools/BuildTools

I edit AssemblyInfo.cs and change an assembly attribute to reference the git commit hash.

This is implemented in C#.

I'll help port/modify it once we know exactly how we want it implemented.