windows platform bug fixes

[majestrate]

replaces #2040 (making new one to not force push to old one)

system layer:

new interface type for interacting with the system layer that hides platform dependent details from caller. this unifies win32 and systemd codepaths.

• [win32] redid all of the win32 service code as it was crufty
• [win32] we now send the right messages to win32 service manager when asked
• [win32] we now shut down correctly on win32 service mode
• [systemd] moved sd_notify into system layer manager implementation

dns:

windows dns was crashy

• correctly how we handle dns lifecycle for win32 since the way they do dns in libunbound for win32 is weird. mostly threading induced race conditions.
• libunbound was crashy on windows with mingw32, patch sent upstream via https://github.com/NLnetLabs/unbound/pull/774

win32 platform code:

resolve threading issues in wintun and windivert, both were race conditions on tear down.

misc:

• rearrange log initialization in daemon/lokinet
• more log/debug statements

remove dead code:

• dns win32 platform
• stray unbound resolver
• unused constants