Allow using ini file to pass options to the installer

[yakky]

Using a ini file will make easier to create repeatable installations

[frost-nzcr4]

I've completed the ini config working task and this branch develop...frost-nzcr4:ini-parse may be interesting for you as well. Also at work I need to get dump of config right after all parsing is completed — dump described here frost-nzcr4/djangocms-installer@ini-parse...frost-nzcr4:ini-dump it helps me partially workaround issue #94: when install failed I re-run it with dumped config.

[yakky]

@frost-nzcr4 this is great! I want those, they look awesome and basically ready for merge (probably just adding ini format documentation)

[frost-nzcr4]

config-file

Sample ini config with all available arguments https://github.com/frost-nzcr4/djangocms-installer/blob/ini-parse/config.ini.sample.
Run:

djangocms_installer --config-file /path/to/config.ini project_name

General config can be cutomised with any available arguments:

djangocms_installer --config-file /path/general-config.ini -p /path/other/proj -s -q project_name

If config.ini not contains no-input = true and -q argument isn't set then one act as a placeholder with default values for wizard.

config-dump

Dumps all arguments to custom config.ini:

djangocms_installer --config-dump /path/config.ini -p . project_name

if installation fails dump can be used to fix some arguments and re-run installer with dumped config:

djangocms_installer --config-dump /path/config.ini --db postgres://wrong-usr:pwd@host/db -p . project_name
# failed
djangocms_installer --config-file /path/config.ini --db postgres://correct-user:pwd@host/db -p . project_name
# succeed

[yakky]

Fixed by #197
A great thanks @frost-nzcr4 for contributing this exciting feature