Add node definitions for new AWG gain nodes as well as compatibility parameters

[nielshaandbaek]

Changes proposed in this pull request:

• Adds the nodes awgs_N_outputs_M_gains_G to the parameter files
• Removes the nodes awgs_N_outputs_M_amplitude from the parameter files
• Adds extra parameters to the AWG8 driver that maps awgs_N_outputs_M_amplitude to awgs_N_outputs_M_gains_M

@MiguelSMoreira

In order for the pull request to be merged, the following conditions must be met:

• travis test suite passes
• all reasonable issues raised by codacy must be resolved
• a positive review is required

Whenever possible the pull request should

• follow the PEP8 style guide
• have tests for the code
• be well documented and contain comments

Tests are not mandatory as this is generally hard to make for instruments that interact with hardware.