Update Greek localization (fixes #72)

[aptiko]

Checklist:

• [ ] All tests are passing
• [ ] I have added any necessary documentation and/or release notes
• [ ] I have followed the commit message guidelines and the "before submitting a pull request" guidelines
• [ ] If I introduced (or abolished) any third-party library, I will write a short paragraph in this PR according to the guidelines
• [ ] I have removed all obsoleted code

[codecov[bot]]

Codecov Report

Merging #377 (3e7db00) into master (8719e62) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #377   +/-   ##
=======================================
  Coverage   97.14%   97.14%           
=======================================
  Files          20       20           
  Lines        1401     1401           
=======================================
  Hits         1361     1361           
  Misses         40       40           

Impacted Files	Coverage Δ
enhydris/admin/station.py	98.70% <ø> (ø)

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