Generalize printLine(), simplify color selection.

Add:
	src/interpreter/shell_graphics.c
		-create generalized printLine() function, which performs all of the
		conditional checks necessary to print a given line of a given type with
		an appropriate prompt and, if possible, color.

	src/interpreter/shell.c
		-enable use of printLine() in src/interpreter/shell_graphics.c to print
		current line by replacing g_enteringCommand with g_currentLineType,
		which represents the type of the current line based on the object-macros
		in src/interpreter/shell.h.