On tplink and orbic, do not overwrite config files by default. There is
a new flag `installer orbic --reset-config` that one can use to restore
the old behavior. This fixes#778, a long-standing issue existent since
0.3.0.
The businesslogic for config file overrides is shared to some degree.
The Install trait from pinephone.rs has been moved out and renamed to
DeviceConnection for that purpose, so that `install_config` can be
shared across installers, which in turn can delegate to the trait for
running commands and copying files. This also works towards #542.
However, the pinephone and other installers have not been adapted to
support --reset-config out of fear of regressions. A future refactor by
somebody with ability to test on pinephone should probably also consider
using the same DeviceConnection impl as orbic, if possible.
