www/tomcat[6|7|8]: Bring improvements from Tomcat[85|9]

• Add options [1] Based on Apache Tomcat documentation guidance, the default web applications have varying degrees of risk, these options will permit users to select which of the web applications should be installed.

• Remove start_precmd from rcfile in Tomcat7 and Tomcat8 [2] This is not being used, users can use ${name}_env to pass variables

• Mark additional config files as @sample [3]

PR: 218865 [1]
PR: 228418 [2]
PR: 229102 [3]
Submitted by: Matt <fsbruva@yahoo.com> [1]
Submitted by: VVD <vvd@unislabs.com> [2] [3]
Reported by: Michael Osipov <1983-01-06@gmx.net> [2] [3]
Approved by: maintainer timeout (ale, > 3 weeks)
Differential Revision: https://reviews.freebsd.org/D16499