add a way to search through the tree

[cdepillabout]

It would be nice to have a way to interactively search through the derivations in the tree.

For instance, if you're trying to build a derivation with musl instead of glibc, you may want to make sure that none of its dependencies are accidentally linked to glibc.

With nix-query-tree-viewer open looking at the run-time dependencies of the derivation, it would be nice to be able to do the following:

1. Press CtrlF, have it pop open a find dialog like the following:

   

2. Type in glibc and hit enter.

3. This takes you to the first derivation in the tree that contains glibc.

4. Hit CtrlI to go to the next instance of glibc, or CtrlP to go to previous instance of glibc.

5. If you've hit CtrlI or CtrlP too many times and the search wraps around, show a message in the status bar.

[cdepillabout]

Alternatively, the search box in the top-right of the nix-query-tree-viewer window could be used for search. I think this makes a lot more sense than having it perform another search for a separate derivation.

[cdepillabout]

@noonien brought up a good point that having a search box that doesn't really "search" is quite confusing: #12.