fix: Added sr-only class to icon only links

[ThomasStivers]

The sr-only class tells bootstrap to present information only to users of screen readers so they are able to identify links represented only by icons.

fixes #1723

Description

ADDITIONAL INFORMATION

• Has associated issue: Screen Reader Accessibility #1723
• Is CRUD MVC related.
• Is Auth, RBAC security related.
• Changes the security db schema.
• Introduces new feature
• Removes existing feature

[codecov]

Codecov Report

Merging #1727 (f06d98c) into master (071e66b) will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1727      +/-   ##
==========================================
+ Coverage   76.77%   76.80%   +0.03%     
==========================================
  Files          56       56              
  Lines        8115     8115              
==========================================
+ Hits         6230     6233       +3     
+ Misses       1885     1882       -3     

Flag	Coverage Δ
python	76.80% <ø> (+0.03%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
flask_appbuilder/security/sqla/manager.py	70.91% <0.00%> (+0.27%)	⬆️
flask_appbuilder/models/sqla/interface.py	78.84% <0.00%> (+0.36%)	⬆️

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[dpgaspar]

Thank you for your contribution, left a couple of comments

[dpgaspar]

@ThomasStivers will be out on the next release