Basic application setup (#1)

This PR contains the work done to define the necessary setup from which the app will be built upon.

To provide further details on what has been done:
* created the app, the unit tests and the UI tests targets in the Xcode project;
* updated the bundle identifiers and OS deployment targets of all targets;
* added a `.gitignore` file tailored specifically for the project;
* added a `README` file that defines in details the goal of the project;
* added the [Swift Format](https://github.com/swiftlang/swift-format) rules that the source code should abide to;
* cleaned the boilerplate source code on all targets.

Reviewed-on: rock-n-code/todos-app#1
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

.gitignore

@@ -0,0 +1,55 @@
+# Xcode
+# General
+.DS_Store
+.AppleDouble
+.LSOverride
+
+# Build generated
+build/
+DerivedData/
+*.o
+*.obj
+
+# Xcode
+xcuserdata/
+*.xcuserstate
+*.xcscmblueprint
+*.xccheckout
+*.xcdebugger
+*.hmap
+*.ipa
+*.dSYM
+*.dSYM.zip
+
+# Workspace settings (shared by team) - keep these under version control if desired
+# Uncomment to keep WorkspaceSettings
+# !xcshareddata/WorkspaceSettings.xcsettings
+
+# Xcode project user files
+*.pbxuser
+!default.pbxuser
+*.mode1v3
+!default.mode1v3
+*.mode2v3
+!default.mode2v3
+*.perspectivev3
+!default.perspectivev3
+
+# Swift Package Manager
+/.build/
+/.swiftpm/
+Package.resolved
+
+# Environment files
+.env
+.env.*
+
+# Archive / export
+*.xcarchive
+
+# Ignore Swift PM artifact indexes
+/.build/checkouts/
+
+# macOS
+.DS_Store
+