Backup Private Key: Integration

[roma219]

• Backup should start after sign up & when clicking button in top dropdown menu
• Successful backup date should be saved in vuex
• TBA

[roma219]

@lapinlapin
Vuex getters:
acc/getBrainkey - get brainkey string
acc/isLocked - if the wallet is locked (needs to be unlocked with passwird to access brainkey)
acc/isValidPassword - getter to check if password to unlock is valid

Vuex actions:
acc/unlockWallet - actions to unlock wallet with password
acc/storeBackupDate - needs to be dispatched after successful backup

If the wallet is locked, there is additional step in backup process, a screen with password input, which is used to unlock wallet (check with special getter at first), and to navigate to the next step if successful.