Add web Images support (proper way)

[ogonzalezadell]

Add support for web images with disclosure indicator

This pull request is a bit more complex :

• Demo project includes JPSThumbnail as a Pod (also SDWebImage as dependency)
• SDWebImage and disclosure indicator has been added
• Demo project has been updated to recommended settings
• Demo project has been updated to display the new features

Notes:

• All changes have been separated in different commits to make it easier to understand
• To run the project first you must run "pod install" command and open the xcworkspace file
• If this Pull request is accepted I would recommend updating the pod version and the readme

[jpsim]

This library has so far been dependency-free, which has greatly minimized the maintenance effort, which is nice given that I haven't personally used this code in several years.

Instead of bundling SDWebImage with this library, are there instead changes that could be made to JPSThumbnailAnnotation that would allow it to better interoperate with whichever networking or image caching library a user prefers and likely already has configured in their project?

I generally prefer making APIs more modular and composable.

[ogonzalezadell]

Okey, I got your point. Have you got any recommendation? If not I will try to work in a more creative way and see if i can make it different.

[jpsim]

Given that you've had more exposure to this library than I have these last few years, I'm hoping you'd have some experience to share. What's preventing this library from working well with an outside image source, like SDWebImage? Does everything work well if you just asynchronously set the image?

[ogonzalezadell]

It seems that is quite difficult to access the ImageView to load images, it should be exposed somehow to allow users to change it manually when the thumbnails are loaded in the map. As I'm not a very experienced developer I do now want to make big "tricky" functions, but perhaps could be a nice idea to implement something similar to tableview delegate methods.