Implement getter and setter for levelrequired. Used by m_modelevel.cpp.

This change is used by m_modelevel.cpp to raise or lower the required permissions to access modes.

Instead of implementing an additional Prefix=>Level method to the config parser, this time I will use

`<define name="founder" value="40000">
<define name="protect" value="50000">`

and reference those through the config itself.

Please note that inspircd still has m_chanprotect.cpp that uses

#define PROTECT_VALUE 40000
#define FOUNDER_VALUE 50000