component.json -> bower.json; adjust jquery to >=1.8.0 <2.1.0

Fixes #6857.
Backports #8050 (`component.json` → `bower.json`) to BS v2.3.x.
Follow-up to #6593 (jQuery 1.9 compatibility confirmation) & #7627 (jQuery 2.0 compatibility confirmation).
Still allows jQuery 1.8 per mdo's comment: https://github.com/twitter/bootstrap/pull/8518#issuecomment-21214011