Embiggen grant image field

[danlipert]

Description

This PR embiggens the grant image field so that any length of filename can be used for the logo

Refers/Fixes

Bug reported by an anonymous user

Testing

tested locally

[codecov]

Codecov Report

Merging #7010 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #7010   +/-   ##
=======================================
  Coverage   26.37%   26.37%           
=======================================
  Files         299      299           
  Lines       29014    29014           
  Branches     4261     4261           
=======================================
  Hits         7651     7651           
+ Misses      21093    21088    -5     
- Partials      270      275    +5     

Impacted Files	Coverage Δ
app/grants/models.py	45.68% <ø> (ø)
app/quests/views.py	16.22% <0.00%> (ø)
app/dashboard/views.py	10.55% <0.00%> (ø)
...rketing/management/commands/no_applicants_email.py	0.00% <0.00%> (ø)
...eting/management/commands/assemble_leaderboards.py	39.73% <0.00%> (ø)

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