[Payment Request] Fixes UI issues raised in UI review

- Splits some of Payments strings into sentence-case and title-case groups.
  in iOS, buttons, labels, and titles must be title-cased and full sentences
  must be sentence-cased.
- Adds leading margin to accepted cards section to align with other texts.
- Sets the text color of the Pay button to white when disabled.
- Sets the secondary text color of the shipping option item to its default.
- Uses the correct blue tint color for the "ADD" text for adding cards etc.
- Uses the correct blue tint color for the editor textfields.
- Makes the secondary text color of those editor fields that push a new VC
  (e.g., "Country/Region*"), light grey.

Screenshots:
https://drive.google.com/file/d/0B-GXJsF3pXyjWHB0RDhNSHFxQzQ/view?usp=sharing
https://drive.google.com/file/d/0B-GXJsF3pXyjYzF5S0M2YWNUZUE/view?usp=sharing
https://drive.google.com/file/d/0B-GXJsF3pXyjWnE4ZEpubVFId2s/view?usp=sharing
https://drive.google.com/file/d/0B-GXJsF3pXyjZm5QMmFHM1ZTYjQ/view?usp=sharing

Bug: 602666
Change-Id: If8eb619bce845037cee2e940b05519813f4d3a2d
Reviewed-on: https://chromium-review.googlesource.com/657803
Commit-Queue: Moe Ahmadi <[email protected]>
Reviewed-by: Rouslan Solomakhin <[email protected]>
Reviewed-by: Tommy Martino <[email protected]>
Reviewed-by: Marc-Antoine Courteau <[email protected]>
Cr-Commit-Position: refs/heads/master@{#502642}
8 files changed