Add dependency on numpy

The ska_tango_base.csp_subelement_obsdevice module imports numpy, but
the latter isn't stated as a dependency of this package. This commit
adds numpy as a dependency of the ska-tango-base distribution.

This problem was found while working on YAN-685.

Signed-off-by: Rodrigo Tobar <rtobar@icrar.org>

README.md

@@ -25,6 +25,9 @@ The ska-tango-base repository includes a set of eight classes as mentioned in SK
 
 ## Version History
 
+#### Not released yet
+- Make dependency on `numpy` python package explicit.
+
 #### 0.10.0
 - Add `DebugDevice` command to `SKABaseDevice`.  This allows remote debugging to be
   enabled on all devices.  It cannot be disabled without restarting the process.

setup.py

@@ -35,7 +35,7 @@ setuptools.setup(
     ],
     platforms=["OS Independent"],
     setup_requires=[] + pytest_runner,
-    install_requires=["debugpy", "transitions", "ska_ser_logging"],
+    install_requires=["debugpy", "numpy", "transitions", "ska_ser_logging"],
     tests_require=["pytest", "coverage", "pytest-json-report", "pytest-forked"],
     entry_points={
         "console_scripts": [