Added new options for post list/grids (#9)
Added filter for elements just before they're used (see desc)

Because elements get established early on in the loading process, it is
best to filter them at that point so it only happens once, and not
every time elements are retreived. However, sometimes you need items
only available later in the WP loading process.

For example -- You want to add an option where the user selects terms
from custom taxo. Taxo isn't registered when initially filtering
builder elements and so now you can use "themeblvd_get_elements" filter
for this -- only use when NEEDED.
Improvements to #9 changes