Cleanup PLUGIN_MODE usage

Cleanup PLUGIN_MODE usage

While modernizing more NULL and BOOL situations, I encountered the following two comments in the
code ...
	`// TODO: Convert to PLUGIN_MODE and fix compile error` and
	`// TODO: Convert bMode to PLUGIN_MODE and fix compile errors`

* Values of type `PLUGIN_MODE` were being stored into `int` variables, often with a `b` prefix
(implying the variables were boolean in nature).
* And values themselves were sometimes `false`, or `1` although sometimes from the `PLUGIN_MODE`
enumeration.
* Value testing often assumed the values were boolean (i.e. zero or non-zero)

* I've changed all appropriate variables to type `PLUGIN_MODE` and used explicit values from the
enumeration in all related expressions.
* I've also taken the opportunity to modernize all member variables in the `PluginForFile` and
`PackingInfo` classes, by adding an explicit `m_` prefix