Refactor do_update_line in inserting mode to reduce complexity.

Extract get_obj_at_point and to_scene_point functionality into
separate class functions making them independently testable as
well as allowing them to be stubbed in tests.

Extracted time limit functionality for callback functions into
a time_limited decorator that gets used by get_obj_at_point.

Work towards #19
Further refactor do_update_line.

Move get_hightower_object_at_point into separate
GetHightowerObjectAtPoint function object.

Moved grid coordinate conversions into scene.

Work towards #19
AppVeyor badge should only care about master branch builds.
GUI test about box.

Added new helper functions to simplify testing of modal
dialogs like the about boxes.

Added test that opens the about box via the help menu,
verifies it opened and then dismisses it with escape.
Add about qt dialog GUI test.

Refined helpers for testing modal widgets
by actually restricting them to modals instead
of any active window.

Added test that opens and closes the Qt about
dialog via the menu and dismisses it much like
the other about box test.

For some reason the - disfunctional anyways - attempt
to clean up self.app during tearDown left the application
in a bad state when called after using a modal widget
which prevented the tests from ever opening a blocking
modal widget after that. Removed this call from tearDown.
Improve test execution speed by removing cargo culted delays.

As the vast majority of our GUI tests aren't relying on an event
loop there is really no need to wait for anything. I only added them
because I saw them in sample test code. Remove all delays not relying
on something happening asynchronously in an event loop and reduce the
delay for the ones that do. This should help our GUI tests scale in
the future as we add more of them.
Enable linting for tests.

Previously tests were excluded from linting. As they
started to accumulate cruft (unused imports, style
differences...) already this patch enables linting them
and fixes all issues that occurred due to this.

This patch contains no functional changes.
Added pylama install instructions.
Update README.md
source now complies pep8 with 79 line limit
Merge branch 'master' of github.com:chris-/LogikSim
Implementing ConnectorItems collision behaviour when drawing lines
added basic AND item
reimplemented selection & moving for single items
implemented selection and movement of multiple objects
logicitems now only use their only bounding box --> to not colide with lines
added detailed selection
grouping update events in selection --> much better scaling
AND item is not resizable
pylama fixes