extending issue 254

[maabdelghaffar]

This PR is to continue working on issue 254 in terms of:

• Allowing the user to set a group of conditions without forcing to pass all of them to Landsat-8 search operator.
• The search operator now constructs the search conditions according to the optionally passed parameters.
• If passed startdate only, it will get all scenes since that date till today (note the filter_max param)
• If passed enddate only, it will get all available scenes till that date (note the filter_max param)
• If passed start and end dates, it will work accordingly to fetch scenes taken between those dates
• And same for cloud_coverage, path and row

[maabdelghaffar]

Right, thanks for the guidance, updated now

[randomorder]

Thank you