Install clang-extra-tools which now contains clang-format.

[ci:skip-build]: already built successfully in CI

Enforced by the new clang-format version.

Two lines above we're already checking if flag_font is set.

This commit was mostly automated using clang-format.

Change local includes from <> to ""

Also remove an unused variable noticed by nsiqcppstyle (unfortunately
not noticed by clang-tidy).

This CI config is based on the travis one. nsiqcppstyle was dropped as
it required python2.

In its place, two clang-based tools were introduced: clang-tidy for some
static analysis, and clang-format for some linting.

Also delete the travis configuration, as it is stale, unlikely to be
used anymore, and prevent it from rotting.

Fixes #4

* added indent file
* added travis files, switch style checking to match charging_sdl
* added editor config
* fixed up code

cleaned up a few memory issues

small fixes and updated cli flags

Added icon for when the device is charging

Added option to use libbattery instead of SDL for battery monitoring