Plugin system draft + example plugin

[nodiscc]

Very rough work in progress. This (will) add a plugin system for page elements. Do not merge.

The example plugin adds a readityourself link for each Shaarli link, pointing to a readable version of the page (example).
The readityourself server URL is configurable.
Requested in sebsauvage#66. To test it, git clone https://github.com/nodiscc/Shaarli shaarli-test; cd shaarli-test; git checkout readityourself

TODO - PLUGIN SYSTEM

• all options should be in options.php, + Move all configuration settings to data/config.php #41
• LINKLIST_PLUGINS should be an array()
  • It's a list of enabled plugins that will get included/run when raintpl generates the linklist
  • adaptable to PAGEHEADER_PLUGINS, EDITLINK_PLUGINS...
• remove the new if condition line 51, instead:
  • loop over all plugin names in the arry, for each, include inc/plugins/$pluginname/$pluginname.html (find a correct location).
  • the <span... print in the example plugin should be in inc/plugins/readityourself/readityourself.html
• test test test
• add more example plugins (archive.org ? qr code?)
• test test
• rebase and squash commits

This method should work for most feature requests in #14, and allows moving some current core items (thumbnails, qr) to plugins. Third party plugins can be cloned in plugins/ and simply enabled in options.php.

Current status: draft draft draft. Give it some time or submit changes to https://github.com/nodiscc/Shaarli on branch readityourself

[nodiscc]

Resuming work on this now. Please do not merge. The pull request is open for anyone to comment on the logic and my crap code skills.

[nodiscc]

Closing this for a clean start in https://github.com/nodiscc/Shaarli/commits/plugin-system