Reorganization of sqlite_base.py

[astafan8]

The reason of this refactoring is to allow database upgraders to have snippets of code from qcodes that are only relevant to those database versions. For example, when we remove layouts and dependencies tables we will still preserve the code that works with them "as is" in a module for the relevant database upgrade, and will change the sqlite API that qcodes uses as we need (this is the reason for Codacy to report problems on this PR).

The new structure is somewhat explained in the top-level docstrings of the new sqlite modules and sub-modules. I also tried to make good commits, so it might be helpful to just follow the commit history to see what happened.

The code has only been moving, and import statements have been adjusted. So, the functionality and bodies of functions are intact.

Note that dataset/sqlite_base.py and dataset/database.py modules are now NOT used inside qcodes, but are left with imported entities to facilitate migration of other dev branches of qcodes, and, unfortunately, some third-party tools. All the new development shall be done in the new sqlite package.

Note imports of two notebooks were updated due to this change.

not gonna do now:

• !!! apply some privatization scheme so that sqlite stuff does not get used all-over-the-place (to-be-discussed offline)
• move sqlite3 adapters and converters into their own module(s)
• go through all of the dataset module and move all sqlite-query code (for example, in experiment container module) to sqlite.*

@QCoDeS/core

[codecov]

Codecov Report

Merging #1570 into master will increase coverage by 0.06%.
The diff coverage is 94.47%.

@@            Coverage Diff             @@
##           master    #1570      +/-   ##
==========================================
+ Coverage   72.12%   72.18%   +0.06%     
==========================================
  Files         105      112       +7     
  Lines       12305    12293      -12     
==========================================
- Hits         8875     8874       -1     
+ Misses       3430     3419      -11

[astafan8]

@QCoDeS/core I would like to try to be annoying and propose to take care of apply some privatization scheme so that sqlite stuff does not get used all-over-the-place in a different PR. So, with your review, please tell if you agree with the structure or not (suggestions/questions are welcome).

[jenshnielsen]

I think the structure is good 👍 My only question is if we should warn on importing from the legacy locations.