#4716. Fixed issues with map details and thumbnail creation in home page

[offtherailz]

Description

Removed unnecessary and remaining double encoding due to the new API entry (PUT with Body, instead of URL encoded value, see #4673).
These caused an effective double encoding of the real respources (previously one encoding was removed by decoding by geostore, but the new API use a JSON as body, so no encoding is necessary anymore) and this made impossible to decode on a second load (only one decodeURIComponent is present, for retro-compatibility, but URLs was encoded 2 times in error.)

NOTE: didn't add unit tests because these where not covered and this part will be replaced soon with the Resource Observable. (see #2908)

Please check if the PR fulfills these requirements

• The commit message follows our guidelines: https://github.com/geosolutions-it/MapStore2/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce? (check one with "x", remove the others)

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

Issue

What is the current behavior?
#4716 comment (thumbnails and details created in home page for maps are not available anymore after refresh)

What is the new behavior?
Thumb and detail card URLs are saved correctly (no double encoding anymore). Decoding is still present for retro-compatibility.

Breaking change

Does this PR introduce a breaking change? (check one with "x", remove the other)

• Yes, and I documented them in migration notes
• No

Other useful information

[coveralls]

Coverage increased (+0.003%) to 84.52% when pulling b2a7cfe on offtherailz:fix_4716_maps into 5147c4b on geosolutions-it:master.