Persist current user's group in local storage

[RichDom2185]

Description

Somewhat part of #2665. The following bug was reported by @lizchow:

Accessing the grading dashboard will default to showing "my groups" for staff, but after refreshing the page, it defaults back to all groups.

The cause was that although the current user and their role is persisted in the browser, the same is not the case for the user's group. As our check involves showing all groups for admins or those without a group, the bug occurs upon the browser refresh.

Solution is simply to persist the group data together with the rest of current user information.

Sorry it took a while, thanks for reporting!

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This PR also replaced deprecated interfaces with their replacements.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Code quality improvements

Checklist

• I have tested this code
• I have updated the documentation

[coveralls]

Pull Request Test Coverage Report for Build 6752262108

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 37.154%

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Totals
Change from base Build 6735695179:	0.0%
Covered Lines:	5707
Relevant Lines:	14431

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💛 - Coveralls

[sayomaki]

Looks good, thanks!