Use sqlite helper plugin and other stuff

An update where the [[sqlite|sqlite helper plugin]] is applied to do all the sqlite work for BlogTNG. The sqlite plugin has already upgrade features and is maintained regularly.

  * This update adds dependency at the [sqlite](https://www.dokuwiki.org/plugin:sqlite) plugin
  * This plugin let you upgrade you from sqlite2 to sqlite3 when available
  * This plugin can only update your database when sqlite2 & sqlite3 are installed. Otherwise you need to upgrade manually, see its instructions.

During upgrade the old sqlite2 version of the database is kept unchanged as `[dokuwiki]/data/meta/blogtng.sqlite`, the new sqlite3 database is now created at `[dokuwiki]/data/meta/blogtng.sqlite3`

Please report all your issues at the https://github.com/dokufreaks/plugin-blogtng/issues please.

There are also some addition changes in the branch. The most important one is that page that are no blog entry, aren't stored anymore in the database.

General changelog: 
  * use sqlite plugin for sqlite handling
  * add configurable defaults values for blog form in edit window
  * max 3 optin mails, not configurable by admin anymore (feature from sqlite3 branch)
  * Store values of blog form only when in edit window a blog is selected
  * remove info from db when wikipage is not blog anymore
  * refresh metadata and db info only for wikipages that are a blog
  * when page is deleted, delete its tags too
  * added comments referer to rss feed (RSS 0.91 & RSS 2.0 only)
  * creating page with newform, uses now namespace templates like manually created pages.
  * newform can have additional fields for tags and commentstatus. `?` is placeholder for the configured default values
  * apply improved comment layout as proposed by hArpanet
  * check security token in admin interface for modifying actions
  * use pagination in all listings of admin
  * use separated count queries to reduce query loads
  * comment previews use correct blog template files
  * `~~READMORE~~` in lists and tables are truncated at nice and correct way
  * all `<blog *>` use now `listwrap`
  * Adding PHPDocs and refactoring code