Adaptation of https://github.com/siamect/proview for slapOS

What works(or at least worked last time i checked):

• using shellinabox
• launching pwra from shell and looking at it over vnc (i used tigervnc)
• launching runtime with a simple plc program (it also starts Status Server which is checked with a promise)

Bugs to fix:

• [test result] While passing tests ok on slapos-sr-testing inside Webrunner, remote testnodes suffer from what looks like a sudden directory disappearance:

2020-04-16 16:22:23,549 INFO     slapgrid_sr: 2020-04-16 16:22:23 slapos[19311] INFO mkdir  /srv/slapgrid/slappart13/srv/testnode/cyl/soft/9dcc2f98adf78c72a92045f224bd7c34/parts/pwr__compile__/proview-63dcc19e71741468e2484ea526db1a54601f4319/rls/os_linux/hw_x86_64/bld/exe/tools_cmsg2c
...
...
...
2020-04-16 16:25:56,253 INFO     slapgrid_sr: 2020-04-16 16:25:56 slapos[37719] INFO /bin/sh: 2: cannot create /srv/slapgrid/slappart13/srv/testnode/cyl/soft/9dcc2f98adf78c72a92045f224bd7c34/parts/pwr__compile__/proview-63dcc19e71741468e2484ea526db1a54601f4319/rls/os_linux/hw_x86_64/bld/exe/tools_cmsg2c/tools_cmsg2c.d: Directory nonexistent

Junk to clean:

• debugging stuff.
• (possibly) LD_LIBRARY_PATH from shellinabox session (it should be no longer needed)
• commits about altering python rpaths (it is no longer needed because a proper order of pycurl loading was restored)

Possible improvements (without altering functionality):

• switch to gtk to improve compilation times (last time this path was blocked by a proview build bug but that may be fixable) since qgtkstyle of qt still uses gtk
• switch from oatchelf to chrpath to depend on gcc less
• find a way to turn off doxygen documentation generation to turn gcc dependency off entirely and remove the second after qt compilation timesink
• ability to download an arbitrary proview-r plc package.

Future directions (with altering functionality):

• fully headless build without any graphical dependencies.
• simulators of modbus-tcp devices for tests.