rename LOBSTER schema names

[phiwuu]

• rename req to requirement
• rename act to activity
• rename imp to implementation
• rename "activity" to "verification"

To prevent breaking changes, support both strings.

This is needed to simplify the usage of the LOBSTER interface. The current shortcuts are not intuitive for our users. Especially act and even activity is confusing.

Note that this change needs to be supported by miss_hit, too.