Milestone filter on todo's
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#### Problem
With many different todo's and issues to keep track of it becomes harder to correctly prioritise and act on them.
#### Proposal
We need a milestone filter on the todo's page, so we can actively filter out all todo's who are not on items not related to any milestone.
Yes we have the `order by priority` sorting option. However this option is very vague in what it does and in that way doesn't provide good feedback..

#### Value
Better visibility on todo's tagged with a certain milestone.. in order to be able to act on those more quickly/easily
cc: @tauriedavis @dzaporozhets @fatihacet @victorwu @smcgivern @JobV
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