Update Postgres.app instructions

- remove version number on git so we don't have to change it all the time
- update file path for postgresql.conf
- configure host for psql
- make the seed section its own section so its not embedded as a code snipppet
Update DEVELOPMENT-OSX-NATIVE.md

- fixed typo with '/temp' to be '/tmp'
- removed capitalization if 'It' on same line since it's not the beginning of the sentence.
Merge pull request #2748 from oblakeerickson/patch-1

Update Postgres.app instructions