Add set -u to frameworks and resources copy scripts

This way, CocoaPods does not have to make assumptions about when to copy things, as the user can then set FRAMEWORKS_FOLDER_PATH / UNLOCALIZED_RESOURCES_FOLDER_PATH for static library targets

This is an optional variable

This variable isn't set by Xcode when running this script.

This case statement handles different iOS device families, for macOS
builds this build setting isn't set.

Turns out that bash arrays are not initialized until they have a single
item. This means this variable is treated as unbound until we add an
item to it. By defaulting this to nothing, this check succeeds even if
no items are ever added to the array.

This is required for `set -u` to work since this variable isn't required
to be set.

This adds `set -u` to both the frameworks and resources copy shell
scripts. This means that if the scripts attempt to reference any
variable that is undefined, they will fail.

[Sandbox] Clean up usage of #local?

Only add resources and frameworks build phase when needed

A recent version of git has changed what whitespace it outputs

This changes the project integrator to only add build phases to the
user's project if there are resources of frameworks that will be copied
in that phase.

Clear input/output paths if they exceed an arbitrary limit

Warn instead of throwing an exception when dev pod's license file is missing

Warn instead of throwing an exception when a development pod's podspec specifies a license file that does not exist

Better static frameworks transitive dependency error checking

Store spec repos in the Lockfile

Always update input/output paths even if they are empty

 [Examples] Get examples building with Xcode 9

[Repo::Push] Allow disabling overwriting published specs

Unique all available pre-release versions when displaying