Assign a default value for display max_seq_items

Perhaps I've opened a dupe issue in the past, can't find it.
pd.options.display.max_seq_items should not be None by default.
It's easy to hang the terminal by repr()ing with some mal-chosen data.
#3426

[cpcloud]

I set mine to 10 by default but that may be too small.

@jreback , @cpcloud , 0.12?

[jreback]

up2u

[cpcloud]

i could take care of this in the pr i have for repring large sequences but i don't think i'm going to be able to finish it by 0.12...

please do. if it doesn't make it, no problem.

[jreback]

@cpcloud 0.13 or push?

[cpcloud]

0.13

[jtratner]

I kinda wish we could add defaults to config options (i.e., if I'm not defined, use this other config option instead), then we could have this default to max_rows. Does add some complexit.

[jreback]

is this the same as max_rows? (or is this applicable for something else?)

[cpcloud]

no this is different

this for repring large sequences (in general, MultiIjndex, Index, lists, dicts, etc)

max rows is for a frame summary