create preliminary FileInput class for ALTO XML

[rlskoeser]

New subclass for alto input

• takes a zip file as input
• field names include section_type
• preliminaryget_text method : iterate over xml files in the zipfile (print out for now)

[rlskoeser]

Here's some of the code in PPA where we're working with files content within a ZipFile, in case it's a helpful example:
https://github.com/Princeton-CDH/ppa-django/blob/0fb7fb9a50429ca26c26d686297cc9b4c521c6a2/ppa/archive/models.py#L1065-L1077

Also recommend looking at the python zipfile documentation.