LP#1775466 Makefile browser client build support

LP#1775466 Makefile browser client build support

Adds an optional --enable-build-web-client ./configure flag for building
the AngularJS and Angular browser clients during Evergreen 'make'.  The
option is disabled by default, since it requires -developer
prerequisites.

Teach make_release to use the new --enable-build-web-client when
building browser clients.

Enable browser client building by default in make_release.  The -c flag
now disables browser client building.

Signed-off-by: Bill Erickson <berickxx@gmail.com>