lib/model, lib/config: Support "live" device removal, folder unsharin…

[AudriusButkevicius]

Purpose

lib/model, lib/config: Support "live" device removal, folder unsharing and folder configuration changes

Furthermore:

1. Cleans configs received, migrates them as we receive them.
2. Clears indexes of devices we no longer share the folder with

Testing

Manual tests, unit tests of questionable quality

[calmh]

Add a // Can't happen or a panic("bug: error in preparing new folder: " + err.Error()) or something here as I was wondering for a while if you'd gone insane to panic on a prepare error then realized it was in New() and should be fine :)

[AudriusButkevicius]

bump

[calmh]

@st-review merge it

[st-review]

@calmh: Merge failed:

$ git fetch -f origin refs/pull/3478/head:pr-3478
$ git fetch -f origin master:orig/master
From github.com:syncthing/syncthing
   0655991..ea87bce  master     -> orig/master
$ git reset --hard
HEAD is now at ea87bce lib/protocol, lib/model: Implement high precision time stamps (fixes #3305)
$ git checkout master
Already on 'master'
Your branch is up-to-date with 'origin/master'.
$ git reset --hard orig/master
HEAD is now at ea87bce lib/protocol, lib/model: Implement high precision time stamps (fixes #3305)
$ git clean -fxd
Skipping repository syncthing/syncthing
Skipping repository syncthing/syncthing-android
Skipping repository syncthing/docs
Skipping repository syncthing/discosrv
Skipping repository syncthing/syncthing-gtk
Skipping repository syncthing/syncthing-inotify
$ git merge --squash --no-commit pr-3478
Auto-merging lib/model/model_test.go
CONFLICT (content): Merge conflict in lib/model/model_test.go
Auto-merging lib/model/model.go
CONFLICT (content): Merge conflict in lib/model/model.go
Auto-merging lib/db/set.go
CONFLICT (content): Merge conflict in lib/db/set.go
Auto-merging lib/connections/service.go
Auto-merging lib/config/wrapper.go
Auto-merging lib/config/config_test.go
CONFLICT (content): Merge conflict in lib/config/config_test.go
Auto-merging lib/config/config.go
Auto-merging cmd/syncthing/main.go
Squash commit -- not updating HEAD
Automatic merge failed; fix conflicts and then commit the result.

[calmh]

@AudriusButkevicius ^ :/

[AudriusButkevicius]

@st-review merge

[st-review]

@AudriusButkevicius: Build status is pending. I'll wait until it goes green and then merge!

[st-review]

@AudriusButkevicius: Build status is failure -- refusing to merge.

[AudriusButkevicius]

@st-review merge

[st-review]

@AudriusButkevicius: Build status is pending. I'll wait until it goes green and then merge!

[st-review]

@AudriusButkevicius: Build status is failure -- refusing to merge.

[AudriusButkevicius]

@st-review merge

[st-review]

@AudriusButkevicius: Build status is pending. I'll wait until it goes green and then merge!

[st-review]

👌 Merged as af3b6f9. Thanks, @AudriusButkevicius!