conda_installer: Include conda in environment

[astaric]

Issue

Standalone Miniconda installer (offline) does not include conda "executable" and does not use the conda-forge channel.

To reproduce use current miniconda installer (on a clean windows installation) to install orange.
Navigate to %LOCALAPPDATA%/Orange/Scripts
conda.bat is not present

Description of changes

Create conda.bat and .condarc files manually

[codecov-io]

Codecov Report

Merging #2616 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2616   +/-   ##
=======================================
  Coverage   74.99%   74.99%           
=======================================
  Files         331      331           
  Lines       58076    58076           
=======================================
  Hits        43555    43555           
  Misses      14521    14521

[astaric]

Another thing that is missing from the current installers is the addition of the conda-forge channel.
The easiest way to do this (without breaking any existing environments) is by creating a .condarc file in the root of the environment ("C:\Users\x\AppData\Local\Orange") with the following content:

channels: 
  - defaults
  - conda-forge

[astaric]

@ales-erjavec I think I'm done. Can you take a look?

[ales-erjavec]

Seems to work OK with conda 4.1, 4.2 and 4.3.