Adding buttons for fitting and rotating page

[bryjamus]

I add buttons to toolbar which are responsible for fitting and rotating page. Fitting page is made by one of tree states:

1. Fit width
2. Fit height
3. Fit best - which use one of above two states depending on control and document scale factor (look at method CalculateZoomMode in PdfRenderer.cs).

[bryjamus]

If changes are ok with you please make new Nuget version after merge.

[bryjamus]

One more think which you should know:

• fit_xxx.png are downloaded from IconArchive and are on LGPL License
• rotate_xxx.png are downloaded from IconArchive and are on CC Attribution 4.0 License

[pvginkel]

Thank you for your pull request. However, the changes to the toolbar should not be added to the project. I know this is a bit confusing to people, and I should really document the reason for this and how you can work around this. I've just now created an issue for this at #41. Please have a look at that for an explanation.

I do however like the best fit change. If it is possible for you to remove the changes to the PdfViewer control, I'm happy to accept the pull request. Sorry for the confusion.

[bryjamus]

I revert changes and implemented only "Fit Best" in PdfRenderer class.

As I understand as you release new version we should use PdfRenderer instead PdfViewer and make our own toolbar for this control?