Replace design assets/links references to MM

[pablofullana]

Review the whole project and update assets, links, strings and anything that may refer to MM

[igorbarinov]

• replace icons to https://www.dropbox.com/sh/f808p8o7eln1x8o/AACn8Znq5r0CdZHKUzg4JgB1a?dl=0
• replace name to Nifty Wallet

[vbaranov]

@igorbarinov

There are missing icons:

• 64 × 64
• 512 x 512

Please ask to add them too.

[igorbarinov]

@vbaranov added to dropbox