Improve header parsing

Until now I used readline to parse the header of a metadata dump.
Unfortunately, some dumps have all the data in one line or only few.
Eventually, this leads to parsing the whole file. The point was to avoid
exactly this. Instead of readline a loop is used in which readchar is
called.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Group snapshots on the importer page

The list of snapshots gets too long with many snapshots. Hence, they are
now grouped.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Use non-whitspace characters to retrieve words

For the accessibility metric I have changed the regular expression to
retrieve words out of a sentence. Instead of w+ I am using now S+. The
overall result seems to be a lot better. For instance floating point
numbers or numbers with delimiter are not split anymore.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Sort snapshots by date

Just added a sort to display the snapshots in a sorted order.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Create metadata record at import stage

For unique metadata records associated with one snapshot the identifier
creation has been moved to the import stage. There snapshot identifier
and metadata record identifier are known as opposed to the default block
that can be provided through Mongoid.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>