Convert to compile with Delphi 12

[delphidabbler]

It's about time this code base was moved to an up to date compiler.

Probably safer to stick to a 32 bit only Windows target to begin with.

[delphidabbler]

Original issue title was "Convert to compile with Delphi 11". Now updated to Delphi 12 since 12 replaced 11 on my dev box.

[delphidabbler]

Because there seems to be a difficulty with VCL forms updating from Delphi XE to Delphi 12, the whole UI needs to be recreated.

Such changes make this a time consuming process. It may not be able to be completed for a while yet.

[delphidabbler]

Experimental code note

I have some test code for this in the Git stash on my main dev box.

There's also a feature branch for this issue on my dev box.

[delphidabbler]

Programs compiled with Delphi 12 require Windows 7 SP1 or later, so won't run on Windows Vista.

Therefore, as part of the conversion process, consider removing the Vista entry from the application manifest file.