Bug 924736 - [Dialer] Incoming call lock screen icons css/animation fine-tune. r=etiennesegonzac,  a=timdream

- 1. Ensure the lock screen handle looks correct on non-320px wide mobile screens.
- 2. Add swipper expending animation while call hang up/pick up triggered.
- 3. Ensure the swipper bar length matches the container perfectly. (call hang up side has 1px mismatched currently).
- 4. Replace the less/greater sign ascii character with image.