Drop use of simplejson

Since json is a standard library as of Python 2.6 and 2.6 is our
baseline target we can drop the need for simplejson.
Imports: Add isort

- Add info for isort in development setup
- Add default config for isort behaviour
  - Ignore a number of files and folders
Imports: sort convert/
Imports: sort tests/
Imports: sort translate/
Imports: sort translate/lang
Imports: sort translate/search
Imports: sort translate/misc
Imports: sort translate/services
Imports: sort translate/tools

No sorting of test_* or commandline scripts
Imports: sort translate/tools/test_*
Imports: sort translate/tools commandline tools
Imports: sort translate/filters
Imports: sort import/storage
Imports: sort translate/storage/test_*
Imports: sort translate/convert
Imports: sort translate/convert/test_*