feat(app): added legacy import link and added fetch balances on mount

[DalderupMaurice]

Description

• Added returning user link below login/register field
• Fetch balances when portfolio tab mounts
• Moved fetching of balances on new blocks app-wide, removing the onmount balance fetch, which crashed the app

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate)

Types of changes

• Chore (tests, refactors, and fixes)
• New feature (adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• I have read the CONTRIBUTING guidelines and confirm that my code follows the code style of this project.
• Tests for the changes have been added (for bug fixes/features)

Documentation

• Docs need to be added/updated (for bug fixes/features)

Closing issues

Fixes #

[codecov]

Codecov Report

Merging #1361 into develop will increase coverage by 0.02%.
The diff coverage is 57.14%.

@@             Coverage Diff             @@
##           develop    #1361      +/-   ##
===========================================
+ Coverage    49.53%   49.55%   +0.02%     
===========================================
  Files          249      249              
  Lines         2150     2153       +3     
===========================================
+ Hits          1065     1067       +2     
- Misses        1085     1086       +1     

[deanpress]

lgtm