fix: use HttpClient for fetching tiles

[zarathourstra]

This fix removes the use of URLConnection for fetching tiles. We use HttpClient instead.
the HttpClient manages its own thread pool but keeping the attributes that configure the internal executor ensures a gentle polling
The client is configured with a 5 sec timeout

Tested on examples by changing dependency path to system targetting local jar built and it works. Hope it works on your side
The exception URISyntaxException related to url malformatting are thrown given that someone can provide custom tile provider

[zarathourstra]

One improvment to consider is to remove static on client and expose a method to change configuration for example by providing custom client
This will enable the flexibility discussed about in issue #127

[msteiger]

Thanks a lot - it looks good on the first glance. Will need to dig a bit deeper, but I'm really busy at work right now, so I might need a few days.