worker improvments bsip add worker type flag

[oxarbitrage]

https://github.com/bitshares/bsips/blob/master/bsip-0028.md

we were discussing with @svk31 and @ryanRfox on the possibility of add worker types to worker object so we can filter and improve listings. flags can be "worker", "bsip", "poll".

[wmbutler]

Nice. I really hope this BSIP eventually sees the light of day.

[ebit116]

support

[pmconrad]

Comment from @abitmore in #40:

• The specification of BSIP's should be determinate, wording like "Possibly allow" is not acceptable.
• I don't think committee should have the right to terminate a worker proposal.