Improve tabbing

[maciaszczykm]

Improved tabbing on deploy page by adding tabindex="-1" attributes. It made Learn more links not accessible via TAB button. It's preffered solution as it was described on https://www.paciellogroup.com/blog/2014/08/using-the-tabindex-attribute/.

Fixes #525.

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This change is

[codecov-io]

Current coverage is 85.99%

Merging #526 into master will not affect coverage as of 44f1857

@@            master    #526   diff @@
======================================
  Files           95      95       
  Stmts          814     814       
  Branches         0       0       
  Methods          0       0       
======================================
  Hit            700     700       
  Partial          0       0       
  Missed         114     114       

Review entire Coverage Diff as of 44f1857

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[floreks]

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Reviewed 1 of 1 files at r1, 2 of 2 files at r2.
Review status: all files reviewed at latest revision, all discussions resolved.

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Comments from the review on Reviewable.io