Don't store access credentials with layouts

[scottsb]

Expected behavior

Credentials which should not be tracked in version control should be stored separately from theme configuration.

Actual behavior

Both credentials (accessToken) and configuration (customLayouts) are stored in the same file (.stencil).

Steps to reproduce behavior

Use Stencil.

[MaxGenash]

@scottsb good suggestion, thanks. I've added a corresponding ticket to our internal board