ui: add notification icon to inform when critical levels of quota usage is reached

[audrium]

closes https://github.com/reanahub/reana-ui/issues/160

• Adds notification icon to the header to inform users when critical levels of quota usage is reached
• Adds same messages to Profile page under Your quota section
• Renames HDD to Disk in Profile page quotas section to be compatible with CLI
• Removes help button from the header

To test:

• Change termination_update_policy to disk,cpu in values.yaml and redeploy
• Run some workflows
• Set some quota limits:

  kubectl exec -i -t deployment/reana-server -- flask reana-admin quota-set -r disk -e john.doe@example.org -l 500000
  kubectl exec -i -t deployment/reana-server -- flask reana-admin quota-set -r cpu -e john.doe@example.org -l 500000

• Verify that notifications appear as expected

Couple of examples:

• If user exceeds the quota limit:

  You've used 105% of your disk quota. Please delete unnecessary workflows.
  You've used 105% of your cpu quota. Please contact REANA administrators for quota limit increase.

• If user reached critical level (>85%) of the quota limit:

  You've used 94% of your cpu quota.
  You've used 90% of your disk quota. Please consider liberating some disk space by deleting unnecessary workflows.

• If quota usage levels are not critical:

  You have no notifications

In the future notifications icon could be used to display things like:

• somebody shared a workflow with you
• "You have 19 running notebook sessions. Please consider closing some."