add support for only, order, order_by, etc. from bib2tpl

[hv15]

We currently do not support the following EXTRA options from bib2tpl:

• group => (none|year|firstauthor|entrytype|$field)
  • is replaced with groupby key which can be (none|year|author|title)
• order_groups => (asc|desc)
  • is not available within bibtexbrowser, use order instead
• sort_by => (DATE|$field)
• order => (asc|desc)
• lang => any string $s as long as proper lang/$s.php exists

without these, filter and sorting is not possible.