BL-6130 Fix Link component
BL-6130 Fix Link component

* normal link UI (pointer cursor and underscore)
   go away if 'href' is undefined on Link
* so we may sure that href is defined, even if its
   optional prop isn't
gmartin7/myBloomFork,gmartin7/myBloomFork,StephenMcConnel/BloomDesktop,StephenMcConnel/BloomDesktop,gmartin7/myBloomFork,StephenMcConnel/BloomDesktop,gmartin7/myBloomFork,BloomBooks/BloomDesktop,BloomBooks/BloomDesktop,StephenMcConnel/BloomDesktop,gmartin7/myBloomFork,BloomBooks/BloomDesktop,BloomBooks/BloomDesktop,StephenMcConnel/BloomDesktop,BloomBooks/BloomDesktop,StephenMcConnel/BloomDesktop,BloomBooks/BloomDesktop,gmartin7/myBloomFork