Remove use of http:// URLs where possible, and update some old links

[Synchro]

I was running some static analysis on a project that uses this SDK, and one thing that always gets flagged is http:// URLs, mostly in documentation. Sometimes these are fine (for example for example.com demos, local tests,, or in XML namespaces), but most of the rest don't really have any excuse, and it's just unnecessary noise, so I thought I'd have a go at fixing them!

Anyway, I updated a whole bunch of these. Some changes might not be appropriate, but obvious ones like entries in CHANGELOG, README, composer.json, are worth taking on. I also updated a few documentation links where they had changed (e.g. sensiolabs changing to symfony).

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[stobrien89]

Hi @Synchro,

Thanks for the contribution! We would accept this, but without the modifications to src/data. Those files have upstream (service) sources and changes to those files originating from the SDK will be overwritten the next time the models are updated.