Show full What's New version in UI

[originalfoo]

This PR changes the version that's shown in-game; instead of the assembly version, it uses the version from WhatsNew.cs which has a manually specified build number.

In mod options:

In game toolbar:

Log file:

Info 0.0539720: TM:PE 11.6.4.2 STABLE - Build 11.6.4.33864 STABLE compiled under C:SL 1.14.0-f4

[kvakvs]

So now Whatsnew.version becomes the primary version, and its typed in manually instead of assembly version?
Versionutil.VersionString might need a comment about this?

[originalfoo]

Well, we need both IMO - the build number in shared assembly info version will change with every build which might still be useful.

For now I just wanted a simple change that's not going to break anything such as other mods - it's only the display string that's changed and anything already reading that already has to parse the version number from the string.

A more nuanced update can come as part of work on #1276 / #685

[originalfoo]

BTW, the main reason I want this basic change is so that users can check if they've got latest mod ver via UI - there's lots of issues recently with Steam not downloading mod updates.

Currently there's no easy way to check visually in-game (11.6.4.2 , 11.6.4.1 and 11.6.4.0 are all shown as 11.6.4). We can find out from logs, but even there it's not trivial as we'd have to compare the build number against releases.