Contrast limit should follow the datatype of the dataset

[edyoshikun]

Current datasets use the channel_name to determine the contrast limits of each dataset. For datasets that are not specified in the dictionary or do not match the channel_name string exactly it will default the settings for 0-65536. For example, if my dataset's channel name is Phase 3D instead of Phase3D (note the space), the clims are set as mentioned above truncating the data, instead of floating points.

The default behavior, if the channel name is not found in the preset dictionary, should use the dataset's datatype.

[edyoshikun]

One interesting behavior is that if you minimize the napari window and then maximize, the contrast limit re-adjusts to float.