Handle simple LINE_PREFIX_BYTES and LINE_SUFFIX_BYTES case

[godber]

ESP_030168_1755_BG12_0.IMG has simple integer values for line suffix/prefix bytes:

/* Image data description. */

OBJECT = IMAGE
    LINES             = 30000
    LINE_SAMPLES      = 512
    SAMPLE_BITS       = 8
    SAMPLE_BIT_MASK   = 2#11111111#
    SAMPLE_TYPE       = MSB_UNSIGNED_INTEGER
    MISSING_CONSTANT  = 16#FF#
    LINE_PREFIX_BYTES = 18
    LINE_SUFFIX_BYTES = 16
    DESCRIPTION       = "Observation image data."
END_OBJECT = IMAGE

This needs to be handled somehow, and it's really a bigger job than just throwing the prefix/suffix away so we can display an image. These prefix/suffix data need to be preserved. For instance, in the example above, the suffix data is dark reference pixels that would be necessary for calibrating the image and is described as follows:

/* Image data line suffix description. */

OBJECT = LINE_SUFFIX_TABLE
    INTERCHANGE_FORMAT = BINARY
    ROWS               = 30000
    COLUMNS            = 1
    ROW_BYTES          = 16
    ROW_PREFIX_BYTES   = 530
    OBJECT = COLUMN
        NAME        = "Dark Reference Pixels"
        DATA_TYPE   = MSB_UNSIGNED_INTEGER
        START_BYTE  = 1
        BYTES       = 16
        ITEMS       = 16
        ITEM_BYTES  = 1
        DESCRIPTION = "Dark reference pixel values produced by masked
                      detectors."
    END_OBJECT = COLUMN
END_OBJECT = LINE_SUFFIX_TABLE

So what needs to be worked out prior to implementing this ticket is the interface we expect to use to access image data while maintaining access to this additional data.

[godber]

The data product can be found here:

http://hirise.lpl.arizona.edu/PDS/EDR/ESP/ORB_030100_030199/ESP_030168_1755/ESP_030168_1755_BG12_0.IMG