kohabug 2186 - improve display of empty import batches

kohabug 2186 - improve display of empty import batches

[1] Display the "No records have been staged" message only
    if no import batches exist.
[2] When displaying a batch that has no bibs in it, display
    a "There are no records in this batch to import".  Also,
    do not display the "import record into catalogue" button
    for an empty batch.
[3] Add CSS class "problem" to both messages.

Documentation changes: minor; only required if screenshots
exist of the manage staged MARC records page that has no
import batches on it.

Signed-off-by: Joshua Ferraro <jmf@liblime.com>