Proper LDFlags use for Version and Build

[thebeline]

Explicitly uses the -ldflags directive for populating Version and Build.

This was KIND of implied in the original comment, but not exactly. There shouldn't be multiple places we have to store the version information. One place is enough.

Ideally, this would be based off from the latest git tag on master, but that is for another day.

[thebeline]

Based on thoughts had while considering #243. There is still more to consider in that regard, but during my research it hit me how we were using -ldflags, but not actually using them the way they are intended.

Further considerations could be put towards the format and contents of Build, but that is for another day.

[thebeline]

Since the latest git tag inside the branch 2.7.0-dev is actually 2.6.1, as of this commit, the OctoScreenInfoBox reads:

OctoScreen
2.6.1
${BUILD_DATE}

Where ${BUILD_DATE} is the date/time that the DEB was built.

The same dev/branch considerations mentioned in #243 apply here: Probably best to tag the dev branch prior to merging into master, or tag the "new dev branch" (if we keep going the route of creating a dev branch for each release) with the target release tag at creation.

So many options, so little time... ${CRYING_EMOJI}

[thebeline]

@JeffB42 - I am rounding back to some of my work here, wanted to check before I merged master into my branches if the PRs and branches are even relevant any more. With regards to this branch, is this something I should test to be sure it behaves as described and re-consider? Or is this no longer relevant?