feat: UI selector for project/dataset

[SanjeevLakhwani]

Follows from #161

• improved over the existing redux over the metadata, reducing more stateful property
• Found a bug with /callback in index.js, it was never being triggered as a specific route as it was being accessed before by :lang param
• provided routing for project/dataset navigation by the format of /p/projecId/d/datasetId, rendered to the level needed
• modified the ui to select project/dataset
• improvided on app structure by having separation of concerns with components and using Outlets and Loaders

[davidlougheed]

please fix merge conflicts.

[davidlougheed]

still many rendering glitches here:

• unneeded margin above project title
• project title and datasets subheading should not be the same heading level
• button margin for "clear selection"
• hover background for dataset goes outside of border radius bounds
• text in header isn't aligned with icon vertically
• I think the node heading should be a bit bigger, and then so should this selector heading in the header

[davidlougheed]

i also get this when I load – no routes match /

[davidlougheed]

[davidlougheed]

lgtm