[#2366] Make arrows smaller and move them around
[#2366] Make arrows smaller and move them around

To avoid overlaps, the arrows are placed at slightly different positions
based on the index of the connector for which we are using an arrow, and
the curviness of the connectors is also changed.

akvo/akvo-rsr,akvo/akvo-rsr,akvo/akvo-rsr,akvo/akvo-rsr