Refactor: Extract function ds_sds_compose_component_add_script_content

This also fixes a leak. The 'component' variable was not freed
before, but it should have been.
session->xccdf.source should never be owned directly.
Drop xccdf_session->filename.
Avoid direct use of xmlReadFile.

Use oscap_source facility instead.

This also fixes a leak when ds_sds_compose_add_component_with_ref fails.
Do not attempt to open SCE script to DOM
Refactor: Merge two subsequent conditions together

Decrease a codebase and increase readability.
Avoid direct use of xmlReadFile

Use oscap_source facility instead.
Avoid direct use of xmlReadFile

Use oscap_source facility instead.
Re-use existing oscap_source to add component with dependencies.
Avoid direct use of xmlReadFile

Make a use of oscap_source facility instead.
Avoid direct use of xmlReadFile

Make a use of oscap_source facility instead.
Avoid direct use of xmlReadFile.

This also changes the oval_result_* structure from array
to oscap_htable. The manipulation is easier and more
straight forward. Additionally, this will allow us to
pass xccdf_session->oval.result_sources directly here.
tests: Check codestyle only in C,C++ sources and header files.
tests: Forbid direct use of xmlReadFile within OpenSCAP project
Refactor: Extract function: ds_rds_create_source.
Avoid direct use of xmlSaveFileEnc.

MAke a use of oscap_source facility instead.