Updated Installation Instruction for FUEL B-REL WP1 (FUEL 7.0 rebasing)

Updated Installation Instruction for FUEL B-REL WP1 (FUEL 7.0 rebasing)

Updates include:
   -  MTU Fix (JIRA FUEL-84)
   -  Updates for FUEL config (admin pwd, HTTP proxy option)
   -  Updates for FUEL 7.0 UI Elements
   -  Tagged areas for updated when ODL is available in next WP
   -  Corrected typo
   -  Changed name installation-intruction
   -  Changed name build-instruction

JIRA: FUEL-84

replacing  change: https://gerrit.opnfv.org/gerrit/#/c/3449/

Change-Id: Ib855c67e7fbe93781a4252f43f2911d9c5fa0645
Signed-off-by: Sofia Wallin <sofia.wallin@ericsson.com>