Add option "Export read(s) consensus" to Sanger Reads Editor

Support "Export read(s) consensus" option in Sanger Reads Editor. This option should be added as an alternative to current behavior.

It's required to add a radio button "Export region" on the "Consensus" tab at the "Export consensus" group. This radio button should have 2 options:  "Export all consensus" (default) - the current behavior and "Export read(s) consensus" with the list of all reads, presented in the current Sanger Reads Editor view (it should looks like the similar list in the "Export" -> "Save subalignment..." dialog in Multiple Alignment). This export type has to export a file with several consensus sequences of mapped reads.