Validate geomap server URL and disable redirects for it

[dontqwerty]

This is the PR fixing issue #319.

Description The function validate_geomap_server_base_url takes the geomap server URL as parameter and checks the following:

• the protocol must be HTTP or HTTPS
• the URL must contain only letters, digits and the following characters $-_.+!*'(),{}|\^~[]`"><#%;/?:@&=
• the URL can not contain query parameters
• the URL can not contain anchors

If one or more of the above checks does not succeed, the function throws an exception.

Furthermore, a modification to the context passed to file_get_contents avoids redirects.

Note An SSRF is still possible, but this solution limits the attack surface without limiting the feature.

[LarsMichelsen]

Thanks for your contribution! :1st_place_medal: