SaveAscii and LoadAscii multiple spectra format needs to be changed

[mantid-builder]

Original Reporter: Keith Brown

This ticket is blocked by :

• TRAC8374

This ticket is blocks : TRAC3493, TRAC7645

SaveAscii outputs a different format if the data is one spectrum rather than multiple. The single spectrum format is good, but the multiple format is useless, not used and defined badly years ago.

Create a new version of Save and Load Ascii, probably inheriting from the first where beneficial, that output multiple spectra by using the single spectra format appended multiple times in the file, with a header to specify the spectra and workspace index.

[mantid-builder]

This issue was originally trac ticket 7732