move speed modifier settings to cheats

[serprex]

left configuring modifier buttons on controls pane

fixes #5326

Build Artifacts

• soh-linux.zip
• soh-windows.zip
• soh-mac.zip

[serprex]

@aMannus let me know if this UI looks good, then can add migration code to make moved cvars cheats

[Malkierian]

UI looks fine, though it's weird those checkboxes are wrapping text like that. Not your issue, though.

[serprex]

Taking advice from @garrettjoecox & reducing to one speed modifier

[serprex]

@Malkierian this PR evolved a lot since you reviewed, both in UI (discussion suggested 1 slider), & config migration

[Malkierian]

1. If you're going to remove the use of MigrationAction in the Migration struct, might as well kill the MigrationAction struct.
2. I'd suggest still using std::string, using empty strings (""), and checking for empty for removal vs renaming. I'm not sure I like the idea of nullptr associated with const char*.

[serprex]

switched away from std::string since we're only calling c_str on them, figured best for data model to match destination interface

[Malkierian]

Hmm. Alright, seems Google says storing and checking nullptr there is standard, so we can keep it.