Replace user.config with a JSON file next to the exe

[danielchalmers]

• Settings are saved as JSON in a file next to the exe, named after it: Network-Monitor-x64.settings for the portable exe, Network Monitor.settings for the installed one. A portable copy keeps its settings when it's moved, and each copy has its own.
• The first time a copy runs, it takes the newest .settings file beside it, so a download saved as Network-Monitor-x64 (1).exe carries on from the old one. Otherwise the installed copy gets its own 4.x settings and position back, and any other copy gets whatever 4.x saved last. 4.x's files are only read. The position is skipped while another copy is running.
• A bad value only resets that setting, an out-of-range size is clamped, and a trailing comma is allowed. A file that can't be parsed is kept as .settings.bad before the defaults are saved over it. Saves go through a temp file.
• If the file can't be written, such as in a folder that needs admin rights, it still starts and warns that changes won't be kept.
• The user.config repair-and-restart is gone. Still a single exe with no libraries.

Release notes: settings now live in a .settings file beside the exe and are brought over from 4.x once. Uninstalling leaves Network Monitor.settings in %LOCALAPPDATA%\Network Monitor, and a portable copy doesn't pick up the installed copy's 5.0 settings.