Cleanup and organize sample apps

applications in `apps/` should be better organized. for example, we could have:
- `apps/samples/` - sample apps which can be used as a base for creating own app (`blehr`, `bleprph`, `blecent` etc.)
- `apps/tools/` - tools to hack NimBLE (`btshell`, `blemesh` etc.)
- `apps/tests/` - various apps used as test app by developers (`bletest`)

Start by inventorying the applications under `apps/` and identifying which belong in `samples`, `tools`, or `tests`. Check all references to their current paths before moving anything. Done means the proposed categories are in place and the applications remain usable from their existing workflows.

Written by the indexing model from the issue text.