Dw refactor compile script

Now models is compiled when using make can also do make model and it will compile:

hw:erldb dhw$ make
 APP    poolboy.app.src
 APP    erldb.app.src
./priv/compilemodel
model_path: "examples/"
################## "Start compiling" ###################
file "tags.erl"
################## "Done compiling" ###################

dhw:erldb dhw$ make model
./priv/compilemodel
model_path: "examples/"
################## "Start compiling" ###################
file "tags.erl"
################## "Done compiling" ###################

Get model_path from erldb.app.src env