This makes the `'r'` hotkey snap the last bar to the middle of the pp
line arrow marker no matter the zoom level. Now we also boot with
approximately the most number of x units on screen that keep the bars
graphics drawn in full (just before downsampling to a line).
Moved some internals around to get this all in place,
- drop `_anchors.marker_right_points()` and move it to a chart method.
- change `.pre_l1_x()` -> `.pre_l1_xs()` and just have it return the
two view-mapped x values from the former method.
It was becoming too much with all the labels and markers and lines..
Might as well package it all together instead of cramming it in the
order mode loop, chief.
The techincal summary,
- move `_lines.position_line()` -> `PositionInfo.position_line()`.
- slap a `.pp` on the order mode instance which *is* a `PositionInfo`
- drop the position info info label for now (let's see what users want
eventually but for now let's keep it super minimal).
- add a `LevelMarker` type to replace the old `LevelLine` internal
marker system (includes ability to change the style and level on the
fly).
- change `_annotate.mk_marker()` -> `mk_maker_path()` and expect caller
to wrap in a `QGraphicsPathItem` if needed.
Tyler Goodlet
Conrad Steenberg