Seperate the generic DAP logic from the (SWI-)Prolog specific semantics

[eshelyaron]

Currently (v0.6.3), the implementation of the DAP specification in da_server/1 is interwoven with logic that is specific to the use case of debugging (SWI-)Prolog programs. It seems desirable to separate these concerns into two components, say dap_server and dap_swipl, such that dap_server will implement only the generic framework for easily adapting debuggers in a manner conforming to the DAP specs, while dap_swipl will encapsulate the specifics of adapting the SWI-Prolog debugger with all of its nitty-gritty details. This will allow for (re-)using the dap_server component for creating DAP servers for any language that is implemented on top of SWI-Prolog with minimal effort, by implementing only the logic that is specific for the target language's semantics. Such languages include s(CASP), CHR, Logtalk and probably more.