Revert "Fix connection to Master Backend where the master IP address is a link-local address"

This reverts commit 7e92707d60a9623e59a4e63d72107fa7df6ef708.
Fix connection to Master Backend where the master IP
 address is an IPv6 address

Similar problems as fixed in 5594a6f32e73b0519b556b63983786a01a0f2228, if MasterServerIP is an IPv6 address or contains a scope Id, it will prevent frontend and slave backend to connect.

Several fixes:
* the master backend detects that it is the master by comparing its IP address with the value stored in the MasterServerIP setting. The comparison is made using strings.
So if MasterServerIP is set to something like 192.168.000.001 it will fail (as we would be comparing with 192.168.0.1). IPv6 can also contains upper or lower case characters.
* In some cases, like gCoreContext control server socket, or connection between slave backends and master backend  would only ever used the IPv4 address. Use IPV6 if available

Add convenience methods:
    QString GetBackendServerIP4(void);
    QString GetBackendServerIP4(const QString &host);
    QString GetBackendServerIP6(void);
    QString GetBackendServerIP6(const QString &host);
    QString GetMasterServerIP(void);
    int GetMasterServerPort(void);
    int GetMasterServerStatusPort(void);
    int GetBackendServerPort(void);
    int GetBackendServerPort(const QString &host);
    int GetBackendStatusPort(void);
    int GetBackendStatusPort(const QString &host);

And use them thorough the code, they will ensure the value read is always correct and usable

Ref #10921
Don’t add port number to myth URL if it’s the default port, makes for cleaner URLs

Also put IPv6 URL in lower-case, I find it prettier
Fix search of image artwork in folder

The first character of the path was dropped, causing the search for images to always fail
Add search for “jpeg” type, and make search for image case insensitive.

Note: That entire code should be re-written