Update to LC08 Surface Reflectance Collection

[ElijahElliotP]

Landsat 8 SR needs to point to ee.ImageCollection("LANDSAT/LC08/C02/T1_L2") and instead points to 'LANDSAT/LC08/C01/T1_SR'

[ElijahElliotP]

Landsat 5 and 7 collections are likewise affected.
In all 3 cases band names are impacted from B# to SR_B# and pixel_qa should become QA_PIXEL in select() calls. It seems sufficient for the moment, in my fork of the repo, to use select() to rename the qa band in sr_standardizeBands(). Similarly, I've renamed bands in this way in sr_standardizeBands()
img.select(['[SR_]*B1', '[SR_]*B2', '[SR_]*B3', '[SR_]*B4', '[SR_]*B5', '[SR_]*B7','QA_PIXEL'], ['B2','B3','B4','B5','B6','B7','pixel_qa']) or simply performing selects with that regex in other functions. I am a bit pressed for time so I have not tested which of the 13 instances of select() strictly need this, but I have example code running now after making these changes.