(Feature) Bulk import whitelist

[fvictorio]

Closes #600.

This is a very basic implementation of the whitelist bulk import. There are some things tan can be improved, but I wanted to make this PR as soon as possible so as to not generate merge conflicts with the work that @fernandomg is doing for #596.

Pending things:

1. Give some kind of feedback to the user. Something like: 300 addresses were added, 20 lines were invalid (or something along those lines).
2. Better validation for addresses. Right now only the length is checked.
3. Better styling. Regarding this, it would be nice to add something like Font Awesome for the icons. We could use it later to replace the images with icons.

[coveralls]

Pull Request Test Coverage Report for Build 1536

• 0 of 34 (0.0%) changed or added relevant lines in 3 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.0004%) to 8.769%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/components/Common/WhitelistItem.js	0	1	0.0%
src/stores/TierStore.js	0	10	0.0%
src/components/Common/WhitelistInputBlock.js	0	23	0.0%

Files with Coverage Reduction	New Missed Lines	%
src/components/stepThree/index.js	1	0.0%

Totals
Change from base Build 1522:	0.0004%
Covered Lines:	252
Relevant Lines:	1955

---

💛 - Coveralls

[pablofullana]

@fvictorio shall we open a new issue for items 1..3 that you mention in this PR description?

[fvictorio]

Yes, I will create them.