Prepare plugin-architecture: Move things around

[nhoening]

Make a plugins-folder (is plugins the best name? Should it be a plugon?) within driveby-sharing.

Make a tt-rss folder therein. Move the greader-import folder to plugins/tt-rss.

Every plugin needs one php-file (e.g. gritttt.php) for basic functionality. Make a README to explain that, maybe an interface:

• do_imports()
• check_login() -> True/False
• insert(url, title, comment)

form.php needs the first two, share.php all three.

New config-option: plugin - this way, gritttt-rss finds the right gritttt.php to use.

The config-options gritttt_url and path_to_ttrss are tt-rss specific. Do we need them/can we replace them oce we are done (they are also used in dialog.js).

[nhoening]

We could name that folder platforms