move all config paths to constants
add system config for identifier type and attribute
check for configuration before first export to gc
rename WrongCredentialsException
password field for passwords in system.xml
save GC company id in config
save code of attribute instead of id for easier handling
add and correct XML paths
create default price list
api returns objects
fix last bugs in price list creation
refactor and use variable instead of getting config every time again
create one vat rate for products
refactored first write
refactor price list creation
helper method for creating descriptions
helper method to create images
helper method to create prices
get company from GC
better error handling