Fix for Issue #467 (Aggregation and metadata issue)

[alexdraconian]

This will fix table aggregation links are stored in metadata. Originally lists and clouds were not rendered metadata, so I assume this line is accidentally excluded in tables.

P.S. It seems SQLite plugin ignores search filter in 'metadata' rendering mode. Because of it, documents with table aggregation may include unnesessary relation data in their metadata. So it's correct that #467 is problem, not intended function.

P.S.2. This code will not 'clear' metadata automatically. Admins must use another plugin for rebuilding metadata if they want to.

[alexdraconian]

Ok, I found real cause of this problem.

When rendering metadata, global $INFO is null. So filter placeholders like $ID$, $PAGE$ cannot be resolved properly(resolved as empty string); This results every pages are returned from SQL query, no matter how filter is set.

So I made changes:

• If $INFO is null, get page information with dokuwiki global function pageinfo().
• Re-enabled metadata rendering for table, list, cloud aggregations.

[alexdraconian]

I'm closing this pull request since there're still some awakwardness in my code. I will re-open in other pull request when I get time to make fix for it.

[alexdraconian]

Replaced with #609.