Fix warning for missing member icon file.
Adjust icon positions in class toolbar.

Without this 1px shift some of the icons will be missing pixels from the
bottom.
Remove extra span from property signatures.

Some leftover from old times - not needed at all.
Eliminate Method- and PropertySignature classes.

Instead the MemberTag class now has two helper methods:

- member_link - for rendering member name as a link.
- member_params - for rendering the params list.

Most of the complexity was really related to rendering the
method signature - all this logic is now in Tag::Method class.