Improve data structure

Currently all the different objects that are stored in the database are stored in isolation and therefor additional code it required to link everything together when data is being displayed or indexed.

The structure should be migrated to make use of relationships to simplify the manner in which the data can then be used.

The new data structure should also:

• use UUIDs for primary ids whether then Integer

• set upstream relationships

• introduce a new object IssueLink to describe links between a build and an Issue.