Added method to count URLs in a frontier

[klockla]

Added a method to count the number of URLs in a frontier with an optional search filter.
Modified ListURLs to add also the optional search filter
Case sensitivity is enabled by default on search filter with an option to disable it

[jnioche]

Let's have a separate PR for making the iterator closeable as it is not just for counting the URLs.
Autoclosable means that the close method is invoked automatically on objects managed by the try-with-resources statement. I don't think we use any try-with.
Why use AutoCloseable instead of Closeable?

[klockla]

Let's have a separate PR for making the iterator closeable as it is not just for counting the URLs. Autoclosable means that the close method is invoked automatically on objects managed by the try-with-resources statement. I don't think we use any try-with. Why use AutoCloseable instead of Closeable?

Separate PR for CloseableIterator in: #115

I will rebase this one after merge of #115

Requested changes have been implemented

[jnioche]

see comments, thanks