LaTeX paper minor revisions

* Add support acknowledgement.
* Remove parens around one reference due to text flow (`\citep` -> `\cite`).
* Add line numbers globally to assist reviewers.
* Correct Makefile to build `all` prior to latex specific script, so figures get moved to `./output/skimage` as expected.

As a sidenote, it appears that while LaTeX lines are now wrapped GitHub is not displaying very helpful diffs within lines. E.g., the paragraph in `latex/usage_education.txt` differs by a single removed character (`\citep` -> `\cite`), but this is not highlighted.