Massive clean up of build.cake

[thecodejunkie]

• Sorted all tasks in alphabetical order (this was driving me nuts, kept scrolling around to find the right ones)
• Fixed the indentation in the entire file
• General formatting changes to make it conform with our usual coding guidelines
• Updated Publish-NuGet task to filter out *.symbols.nupkg files
• Removed Nuke-Symbol-Packages (nothing was calling it)
• Removed Mono task (nothing was calling it, not even from build.ps1/sh)
• Added section dividers between helper functions, tasks etc
• Moved helper functions to the bottom of the file and make them static
• Updated UpdateProjectJsonVersion function so it only updates the first version-attribute

I have executed all the tasks locally on my machine to make sure they work and do not throw any errors.

[thecodejunkie]

Ran the script from Windows

ℹ️ We're seeing the weird net452 dependencies because this isn't building against latest master, but it will when we put out -clinteastwood