getSRcollection: SR Collection
In IFGI-Project/LandTendR-Package: LandTrendR Algorithm in R

This function search for the images and create a ee.ImageCollection for each sentinel mission L05,L07,L08. This function also applies the Image preparation function

1	getSRcollection(year, startDay, endDay, sensor, aoi)

`year`	this parameter is automatically and refers to each year from Start Year and End Year
`startDay`	this parameter refers to month and day of the starting year
`endDay`	this parameter refers to month and day of the ending year
`sensor`	this parameter refers sensor in this case either L08, L07 or L05
`aoi`	this parameter refers Area Of Interest and constrain the retrieve images to the AOI.