remove invoke from code and dependency (closes #72)

[ghost]

I tried to remove all invoke dependencies.

Mostly I was lazy and just changed it for the subprocess equivalent, althought I am sure that stuff can be done without invoking the likes of mv and sed (which makes this part of code linux only, btw.)

Reason for not wanting invoke: It is not easily found in distributions, and has quite some shadowy sides.

[toirl]

I have tried this version but I have some problems running at least one command:

agrav-admin fixtures load --path ../demodata                                                                          26.Jul.17 10.00
sed: -e Ausdruck #1, Zeichen 1: Unbekannter Befehl: `''
sed: -e Ausdruck #1, Zeichen 1: Unbekannter Befehl: `''
Loading data in 
Loading fixture 0_users.json
Traceback (most recent call last):
  File "/home/torsten/Entwicklung/ringo-apps/agrav/env/bin/agrav-admin", line 9, in <module>
    load_entry_point('agrav', 'console_scripts', 'agrav-admin')()
  File "/home/torsten/Entwicklung/ringo-apps/agrav/lib/ringo/ringo/scripts/admin.py", line 356, in main
    args.func(args)
  File "/home/torsten/Entwicklung/ringo-apps/agrav/lib/ringo/ringo/scripts/fixture.py", line 13, in handle_fixture_load_command
    args.config,modul,fixture])
  File "/usr/lib/python2.7/subprocess.py", line 711, in __init__
    errread, errwrite)
  File "/usr/lib/python2.7/subprocess.py", line 1343, in _execute_child
    raise child_exception
OSError: [Errno 2] No such file or directory

On master exact this code works as expected.

[ghost]

The command "agrav-admin" was not found.

Apparently invoke automatically adds some (to me, unknown) paths to sys.path, so that an executable will be found if in those paths (probably somewhere in .virtualenv/...?) .

Subprocess takes the system's $path.

I am currently not sure how to solve this, as I don't know where ringo places these binaries, and I don't really want to take "just some binary that is conveniently called like the file I am looking for".

[g-tom]

The command "agrav-admin" was not found.

I suspect there's any good reason to use an applications own user interface inside that very same application.

Instead of invokeing each other, the *-admin commands should be able to use the Python-API directly. Or do I miss something here, @toirl?