Duplicated WMS params lowercase vs uppercase

[pelord]

Please check if the PR fulfills these requirements

• The commit message follows our guidelines:https://github.com/infra-geo-ouverte/igo2/blob/master/.github/CONTRIBUTING.md#git-commit-guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

What is the current behavior? (You can also link to an open issue here)
Some wms params were duplicated.

**What is the new behavior?
Openlayers strictly interpreting wms params in uppercase. We now redirect all wms params to uppercase.

In case of lowercase user defined wms params, all users wms params will be kept. But every params will be converted into uppercase.

In case of duplicated param (uppercase & lowercase), the priority remain to the lowercase property (or the property containning less upercase letters). In the next example, the priority to this user defined property is accorded to layers

ex:

        "params": {
          "LAYERS": "telephone_urg",
          "lAYERS": "telephone_urg",
          "laYERS": "telephone_urg",
          "layERS": "telephone_urg",
          "layeRS": "telephone_urg",
          "layerS": "telephone_urg",
          "layers": "telephone_urg"
        }

Does this PR introduce a breaking change? (check one with "x")

[x] Yes
[x] No

For wms params defined bycode, the wms interface params are now in uppercase.

[pelord]

Also fix

• param FEATURE_COUNT in double in getFeatureInfo call #364
• problem on call v1.1.1 service, param SRS vs srs #489