Support imports wrapped in macros

[FranzBusch]

Brought up in this PR: #82

We have the use-case where we have certain import statements wrapped in #if macros to only import them in e.g. debug builds. Mockolo is right now picking up every branch it would be great if it would retain the macros in the generated code as well.

[elsh]

Triaged

[elsh]

Resolved https://github.com/uber/mockolo/releases/tag/1.2.1

Note that this is fixed only when the swiftsyntax parser (default) is used. If --use-sourcekit option is used in the commandline, macro will still be ignored (this requires extra parsing as sourcekit doesn't detect #if macros; this will be looked into in the future only if necessary).