rename r.sentinel.* and r.modis.* being part of imagery modules

[martinl]

In OSGeo Code Sprint 2018 has been decided that GRASS MODIS and Sentinel Addons modules will be moved to imagery group. It means renaming

• r.modis* -> i.modis*
• r.sentinel* -> i.sentinel*

[martinl]

In 72405:

rename r.sentinel -> i.sentinel (work in progress), see #3522

[martinl]

In 72406:

rename r.sentinel -> i.sentinel (work in progress), see #3522

[martinl]

In 72407:

rename r.sentinel -> i.sentinel (done), see #3522

[martinl]

Done for sentinel:

• https://grass.osgeo.org/grass74/manuals/addons/i.sentinel.download.html
• https://grass.osgeo.org/grass74/manuals/addons/i.sentinel.import.html

[martinl]

In 72409:

i.sentinel: fix fisrt keyword, see #3522

[martinl]

In 72410:

Add r.sentinel info to inform user that addons has been renamed, see #3522

(see r72411 for fix)

[martinl]

For backward compatibility I added raster/r.sentinel/Makefile to inform user about renaming. It works on Linux (compilation performed on client machine) only

g.extension r.sentinel 
WARNING: Extension <r.sentinel> already installed. Re-installing...
Fetching <r.sentinel> from GRASS GIS Addons repository (be patient)...
Compiling...
Makefile:2: *** Extension has been renamed to i.sentinel.  Stop.
ERROR: Compilation failed, sorry. Please check above error messages.

we need to implement better logic for G7:g.extension.

[lucadelu]

In 72415:

r.modis: renamed to i.modis, see #3522

[martinl]

In 72439:

i.modis/i.sentinel: fix r.* leftovers, fix #3522