Added back NIH structure resolver service

This is ported code from Avogadro 1, just the NIH structure resolver
right now. Added a progress dialog, and improved error detection.

Change-Id: I722aa8eba14992d7b6c4c8094c0d979784f5c5fb
Shorten line lengths in ported code.

Change-Id: Ib1a38183425c24009a97115fe138cbd6cd84942c
Merge topic 'online-databases' into master

7afa55e7 Shorten line lengths in ported code.
c8bf6462 Added back NIH structure resolver service