Support for processes that are inactive by default

Ability to list a process in invoker.ini, but not have it autostarted by default
```
[postgres]
command = postgres -D /usr/local/var/postgres

[redis]
command = redis-server /usr/local/etc/redis.conf

[elasticsearch]
command = elasticsearch -f
autostart = false
```
`add` command can be used to start inactive processes later
```
invoker add elasticsearch
```