Maintenance release for 2.51 branch

Highlights:

• Simplified installer - Git and KDiff3 installers are no longer installed as part of GitExtensions's installation. The user will have to install external apps and tools separately.
• Fixes to address a number of layout issues for high DPI monitors.

Features:

• Remove Git and KDiff3 from installer 2.51 - PR 4933
• Check for recommended Git version 2.51 - PR 4932
• Check for recommended Git version - PR 4929
• Delete TAGMESSAGE after tag command completes - PR 4792
• fix: FormFixHome is messed up HiDPI - PR 4780
• fix: FormRemotes is messed up on HiDPI - PR 4779
• Fix avatar under high DPI - PR 4711
• Remove Git from installer package - Issue 4515

Fixes:

• Shell start script failing if run from a different directory - Issue 4975
• Crash when you click on the Commit tab - Issue 4956
• "Reset all changes" not working when "Refresh dialog on form focus" true - Issue 4907
• CommitPickerSmallControl broken under high DPI - Issue 4862
• Init wrong folder - Issue 4855
• "Clone repository" form layout broken at high DPI - Issue 4776
• Git config diff.noprefix true option breaks most of GitExtensions functionality - Issue 4392
• When creating an annotated tag, a TAGMESSAGE file is left in the repository - Issue 4358
• "Open local repository" layout broken at high DPI - Issue 4174
• High HDPI is really messing up the display of screens - Issue 4099
• "Clean working directory" form layout broken at high DPI - Issue 3828