Small refactoring

[churkin]

\cc @inikulin

I think it is more logical.

[inikulin]

Tests fail due to incorrect ES6 syntax

[inikulin]

Moreover more likely es7.classProperties will not make it (see: babel/babel#1990), so there will be a task to remove them completely from the codebase.

[inikulin]

Issued a bug: #37. @churkin Can you do the same for the hammerhead?

[churkin]

Of course DevExpress/testcafe-hammerhead#29

[inikulin]

I think since it's constants anyway we will replace it with the instance vars, e.g.:
static TIMEOUT = 123; -> this.TIMEOUT = 123;. It's also will simplify some tests, since we will not need to restore constant var value.

[churkin]

In this case "var instanceCount = 0;" is a real static field :)

[inikulin]

Yes, this case is an exception. But currently we've used static fields only for the constants which can be modified for testing purposes.