Fixed a bug with non-working Shell tab (previously, BACKEND_PREFIX wasn't respected

Revert "Fixed mess related to #51. Paths are relative and BACKEND_PREFIX might contain / or might be an empty string"

Revert "Reverted a42a45e which broke webshell and vnc. We decided in ticket #51 that paths are relative and BACKEND_PREFIX should be absolute, see also 4ee231bf5ddc"

Fixed mess related to #51. Paths are relative and BACKEND_PREFIX might contain / or might be an empty string

Reverted a42a45e which broke webshell and vnc. We decided in ticket #51 that paths are relative and BACKEND_PREFIX should be absolute, see also 4ee231bf5ddc

Fixed a bug that was introduced when BACKEND_PREFIX was changed; Moved BACKEND_PREFIX prepending out of widgets.Shell

Fixed a bug in NewVmController: BACKEND_PREFIX was ignored when submitting the new VM form

Removed the trailing slash from BACKEND_PREFIX: some URLs already have a leading slash

Used the new makeColumnRenderer util in VmListTab to make gauge columns

Added the makeColumnRenderer util

Merge branch 'vm-map'

Added ENABLE_VMMAP_REFRESH, ENABLE_VMMAP_TAG, ENABLE_VMMAP_RESIZE, ENABLE_VMMAP_MIGRATE flags.

Added ENABLE_VMMAP and ENABLE_VMMAP_TOOLBAR flags, which are "true" by default.

Do not allow VM migration to the same machine.

Use DISABLE_VMMAP_TOOLBAR = 1 in config.js to disable the vmmap toolbar.