Charge List list item layout updates

Charge List list item now displays coordinates (x, y) instead of x
position: ... , y position: ...

Updated charge list list item for a line charge to show angle, and
start/end coordinates. Now also updates live when any attributes change
and the list element is expanded.

Tested and fixed small bugs for adding line charges by start point,
length, and angle

Removed redundant add negative element functions and changed add
positive element functions to take in a polarity parameter. For example:
to add a negative element, pass in "-1" to function