Remove bamboo specific stuff

[ds58]

Changes:

• Remove any implementation of the legacy "Nexus REST API" for integration number
• Removed the tests for the REST API
• Remove concept of integration number
• Remove JCenter
• Removed commented code regarding legacy source sets
• Removed concept of "branch builds" and "bamboo builds"
• Removed most of the composite build snapshot dependency resolution, as it was just for bamboo
• Remove html library (unirest-java)
• Rename nexusUsername, nexusPassword to ihmcNexusUsername, ihmcNexusPassword (only in code, the properties stay the same)
• Remove the ability to configure the nexus URL; it is ihmc specific, ihmcNexusUrl
• Removed extra whitespace in IHMCBuildExtension.kt, minor formatting

[ds58]

@calvertdw Sorry, didn't mean to add you yet

[calvertdw]

I put the remove JCenter on develop, since that one is a known isolated good thing