Improve "Fetch Sequence from BLAST Database" dialogs

Make sure to modify both BLAST and BLAST+ dialogs.

1. Rename the dialog to "Fetch Sequences from BLAST Database" (i.e. plural).
2. Improve the dialog layout
3. Provide a default "Output path". For example, you can put the output to a subfolder in the standard UGENE file storage folder (.UGENE_files).

You should take into account that:

1. Several runs of the dialog can be done
2. The folder can have not enough priviledges to read/write the folder