LaTeX writer: Fix tables

- [x] Fix a bug introduced in 66378062b622b0815a1a2ddce5d557e3ad13330c, which causes the table caption to repeat across all pages
- [x] Address the issues discussed [here](https://groups.google.com/forum/#!msg/pandoc-discuss/qMu6_5lYy0o/ZAU7lzAIKw0J) regarding the extra vertical space
  - [ ] NOTE: This will cause multiline table cells to appear unpadded. See http://tex.stackexchange.com/questions/34971
  - [x] Use [`\tabularnewline`](http://tex.stackexchange.com/questions/78796) instead of `\\`.