Feature request: globally configurable yes/no to downloads

[flauschzelle]

(first discussed in #94)

A possibility to get rid of the questions waiting for user input would be nice for (at least) the following use cases:

• leave the script running unattended while being afk or otherwise distracted (big archives can take a while to parse)
• automate parsing of several archives if one has many twitter accounts to parse
• re-run the script whenever new features have been added and avoid answering the same questions every time

@timhutton suggested this in the previous discussion:

How about this instead:

• We keep a single enum/int in the script for [ never_download, always_download, always_ask (default) ]

• We print out at the end that there are flags you can set in the code if you want to get rid of the questions.

• Obviously the flags you set will get overwritten by a new version but I think that's reasonable because they may no longer be valid anyway. Or if we really think that's a burden, would maybe consider loading them from a config file if present, and document it in the script.

• At the same time we work to reduce the number of questions asked. For example: merge the download of handles for followings and DMs (leaving followers separate, unless small in number).

(just repeating that here for easier reference)