Move statistics URLs into own statement

This is part of an effort to make the URL configuration and the control
package more readable and maintainable. I double checked, that all
catmaid.control namespace imports removed, where not in use in other
places.

This commit relates to issue #570.
Refer to annotation related URLs explicitly in own statement

This is part of an effort to make the URL configuration and the control
package more readable and maintainable. I double checked, that all
catmaid.control namespace imports removed, where not in use in other
places.

This commit relates to issue #570.