hardcoded references to hack folder #5752

There are several places in DFHack that assume that the hack folder is in the current working directory, an assumption that we can no longer assume to be true. These hardcoded references need to be rewritten to use Core::getInstance().getHackPath().

There is one library reference:

• library/DFSteam.cpp

There are three plugins:

• plugins/dig.cpp
• plugins/orders.cpp
• plugins/pathable.cpp

I didn't find any in Lua scripts - it appears that all Lua scripts are already using getHackPath