feat: Added basic span handling in store

[mitsuhiko]

This is not really useful as it stands, I think we need to rethink this a bit
but it's good enough for now I belive.

This depends on getsentry/relay#179

[mitsuhiko]

I hacked this together to make session store work but I'm not sure this makes any sense for a longer term solution.

[mitsuhiko]

@alex-hofsteede There is a dummy function that gets invoked now doing nothing.

[HazAT]

@mitsuhiko The rust normalization strips away spans.

{u'_meta': {u'spans': {u'': {u'err': [u'invalid_attribute']}}}, ...

[mitsuhiko]

@HazAT any chance you are running an old version of semaphore? Spans were added a while back: getsentry/relay@aa3b92b

[HazAT]

@mitsuhiko I just ran make develop on this branch.
It's probably because I don't have semaphore installed with editable or something.

[mitsuhiko]

I think that might be because this branch is outdated in comparison to master. Merge master in, make develop and that should fix it (i hope).

[HazAT]

That fixed it, rebased master and force pushed.

[alex-hofsteede]

@mitsuhiko I'm going to take this over and see if I can get the events sent into eventstream/kafka.