Tests improve coverage

[jankapunkt]

Intends to improve test coverage to such an extend, that we can safely refactor code to full ES6 without regressions

Also found and fixed additional issues:

• removed old unsused gulp files
• bas64 support for EJSON added (uses the same package as React Native), also browser compatible
• EJSON.equals fails to compare Array and Object if first param is Object and second one is Array this is actually an issue with the original EJSON code and I already filed a bug to the Meteor project
• added unit tests for selector.compileSelector and selector.compileSort
• compileSelector used in $where a fallback if argument is not a function, that relied on the Function constructor, which is replaced now with an arrow function closure
• added unit tests for all transaction types

What remains to be done but is out of scope for this PR:

• testing integration with RN and RN-Meteor
• moving all code to es6; remove decaffeinate autocode (suggested by commets)
• update lodash and eventemitter3 (vulneraibilites!) but that requires careful crafting as they have partially different apis (two/three major version differences)
• add GitHub CodeQL to CI to find potential vulnerable code definitions not picked up by tests or linter

current coverage (updated on each push):

--------------------------------|---------|----------|---------|---------|---------------------
File                            | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s   
--------------------------------|---------|----------|---------|---------|---------------------
All files                       |   91.86 |    90.73 |   94.11 |   92.04 |                     
 EJSON.js                       |   98.91 |    98.49 |     100 |     100 | 140,190             
 MemoryDb.js                    |   94.93 |    88.23 |      90 |    94.8 | 32-36,59,68         
 NullTransaction.js             |     100 |      100 |     100 |     100 |                     
 ReadOnlyTransaction.js         |     100 |      100 |     100 |     100 |                     
 ReadTransaction.js             |     100 |      100 |     100 |     100 |                     
 SynchronousWriteTransaction.js |     100 |      100 |     100 |     100 |                     
 WithObservableReads.js         |   92.85 |    83.33 |   85.71 |   92.85 | 30,60-61            
 WithObservableWrites.js        |     100 |      100 |     100 |     100 |                     
 WithReactMixin.js              |    9.52 |        0 |       0 |    9.52 | 11-81,89-92         
 WithServerQuery.js             |   85.93 |       80 |   78.57 |   85.93 | 26,117-126          
 WriteTransaction.js            |   89.28 |    83.33 |     100 |   89.09 | 86-87,92-96         
 selector.js                    |   96.52 |     92.1 |     100 |   97.84 | 417,421-423,495,659 
 utils.js                       |   96.09 |    91.89 |     100 |   95.93 | 161,214,225,252,300 
--------------------------------|---------|----------|---------|---------|---------------------

[jankapunkt]

@TheRealNate did you get a chance to review this one?

[TheRealNate]

Hey @jankapunkt, sorry about the delay. This is clearly a lot of work! These look good to me, feel free to merge whenever erady.