refactor figures

...ts.xcassets/lettermetaphor/postcard.imageset/postcard.png

...sets/lettermetaphor/postcard_small.imageset/Contents.json

...lettermetaphor/postcard_small.imageset/postcard_small.png

...termetaphor/postcard_small.imageset/postcard_small@2x.png

...termetaphor/postcard_small.imageset/postcard_small@3x.png

enzevalos_iphone/Assets.xcassets/padlock/Contents.json

...hone/Assets.xcassets/padlock/Image.imageset/Contents.json

...Assets.xcassets/padlock/Image.imageset/padlock_secure.png

enzevalos_iphone/CryptoObject.swift

enzevalos_iphone/DataHandler.swift

enzevalos_iphone/MailHandler.swift

enzevalos_iphone/TempAttachment.swift

enzevalos_iphoneTests/testMails/attachment.eml