pokedex/main.py -
  create_parser() -
    Change the help message for the langs argument in the dump subparser
    to show the actual default and state that the 'all' and 'none' codes
    cannot be used alongside other codes.

  command_dump() -
    Check if 'all' or 'none' codes are passed alongside other codes. If
    they are, error message is printed and program ends.

pokedex/db/load.py -
  dump() -
    Add check if langs code is 'all' or 'none'.
    If langs wasn't passed to the parser or 'all' was passed (they are
    the same since the default is 'all'), then everything will get
    dumped to the csv files.
    If 'none' was passed to the parser, then nothing new should be
    dumped to the csv files.

pokexed/.travis.yml -
    Re-added 'pokedex dump -l all' that was previously remove on
    77e3d9d

Resolves: veekun#295

All changes requested in PR 17f3624

 ### pokedex/main.py -
 #### create_parser() -
- Change to langs argument reverting the help message to the original
one but changing the default to 'all'.
 #### command_dump() -
- Add check for 'all' langs code instead of in the load.py file.
- Add/fix comments.
---
 ### pokedex/db/load.py -
 #### dump() -
- Remove unneeded check for 'all' langs code since not it is checked in
the main.py file.
- Reword comment of what happens when the 'none' code is passed.

 ### pokedex/main.py -
 #### create_parser() -
- Change the default in the the help text for the `-l` argument in the
`pokedex dump` parser.

 #### command_dump() -
- Change the functionality of `pokedex dump -l none` to be the same as
entering `pokedex dump`.

---

 ### pokedex/db/load.py -
 #### dump() -
- Change the functionality of the dump command to work the way that the
help text says it should.
- Tables always dump official languages.
- If there were any `langs` passed, then the official languages plus the
specified `langs`  will be dumped from the tables that have a
'local_language_id' column.
- If `pokedex dump -l all` is passed then all the languages (official
and unofficial) will be dumped.
- If the table doesn't have a 'local_language_id' column, then all the
rows will be dumped.