Add ROTATE_180 constant that rotates the screen 180 degrees to allow screen to be mounted inverted

[ClevelandTechnologist]

…mounting the screen inverted

Fixes #<GitHub-issue-number>.

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<Description of and rationale behind this PR>

[ClevelandTechnologist]

I'm working on my own variation of the desk clock, but I ended up with a setup that has the screen pins at the top. So, I created this patch to support rotating the screen 180*.