[Upd] Add better authentication for RDF4jModule

[Matthew-Kulich]

Related to this #29 .

[blcham]

I suggest to implement it little different way.

Have a module with param like following:
:m rdf4j-module:p-rdf4j-secured-username-variable "uclUsername"
:m rdf4j-module:p-rdf4j-secured-password-variable "uclPassword"

And then have config-core.properties providing those variables as you implemented, i.e.
variable.assignment.uclUsername=heslo-ucl
variable.assignment.uclPassword=heslo-ucl

And having ConfigCoreProperties some method that return those variables, e.g.:
Map<String, String> getConfigurationVariables()-- but i would trim "variable.assignment" part out of it.

[blcham]

Please, have a look at my last review, I think we did not understand each other, sorry for that.

I was expecting this module to have new parameter called p-rdf4j-secured-username-variable, i.e. I was expecting that I will find out following code:

    static final Property P_RDF4J_REPOSITORY_NAME = getParameter("p-rdf4j-secured-username-variable");
    private String rdf4jSecuredUsernameVariable;

[Matthew-Kulich]

The simple solution is implemented and merged here #146.

This PR will be finished later.