Integrate tlbmc append mode

Defers tlBMC route regsitering, so that the order becomes:
1. gBMCWeb routes
2. tlBMC routes
3. tlBMC appends
4. gBMCWeb appends

Tested: see cl/850392562

Change-Id: I616f9235a1ee9260881d49252a38083927f047ec
Signed-off-by: Nan Zhou <nanzhou@google.com>