Fixed doc logo size

[bksahu]

This PR fixes the following

• Reduces the size of the Logo in the Docs
• Added doxygen log file to the gitignore

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PR Checklist

• Correct base branch selected? develop for new features and bug fixes too. If it's
  part of a hotfix, it will be moved to master during it.
• All tests still pass. Check the developer manual about Running the Tests. There
  are Travis tests that cover the most important things however, and you are
  welcome to rely on those, but they might not cover enough.
• Ideally new features or fixed regressions ought to be covered via new tests.
• Ideally new or changed features have documentation updates.

[kayhayen]

Very nice to fix this annoying thing, merging right away.