Merge home page and `All Versions` of Bluemix CLI repo into docs

[archerzz]

Requirement

As part of our refactoring on Bluemix CLI installation experience, we decided that:

1. We should not keep duplicated contents in both Bluemix docs and home page of Bluemix CLI repo
2. We should remove All Versions tag on Bluemix CLI repo, and merge its contents into Bluemix docs.