add mandatory alt attributes for images (fixes html5 validation errors)
add mandatory alt attributes for images (fixes html5 validation errors)

conorsch/securedrop,jeann2013/securedrop,harlo/securedrop,pwplus/securedrop,jaseg/securedrop,pwplus/securedrop,kelcecil/securedrop,jaseg/securedrop,kelcecil/securedrop,heartsucker/securedrop,jeann2013/securedrop,ageis/securedrop,GabeIsman/securedrop,pwplus/securedrop,harlo/securedrop,garrettr/securedrop,jaseg/securedrop,kelcecil/securedrop,kelcecil/securedrop,ageis/securedrop,jaseg/securedrop,heartsucker/securedrop,GabeIsman/securedrop,harlo/securedrop,kelcecil/securedrop,micahflee/securedrop,jrosco/securedrop,ehartsuyker/securedrop,ageis/securedrop,GabeIsman/securedrop,kelcecil/securedrop,jeann2013/securedrop,jrosco/securedrop,ageis/securedrop,heartsucker/securedrop,jeann2013/securedrop,GabeIsman/securedrop,conorsch/securedrop,jrosco/securedrop,GabeIsman/securedrop,ehartsuyker/securedrop,jeann2013/securedrop,harlo/securedrop,harlo/securedrop,pwplus/securedrop,garrettr/securedrop,conorsch/securedrop,ehartsuyker/securedrop,garrettr/securedrop,micahflee/securedrop,pwplus/securedrop,harlo/securedrop,jeann2013/securedrop,chadmiller/securedrop,jrosco/securedrop,GabeIsman/securedrop,conorsch/securedrop,micahflee/securedrop,ehartsuyker/securedrop,conorsch/securedrop,jaseg/securedrop,garrettr/securedrop,chadmiller/securedrop,chadmiller/securedrop,ehartsuyker/securedrop,chadmiller/securedrop,heartsucker/securedrop,chadmiller/securedrop,chadmiller/securedrop,jaseg/securedrop,ehartsuyker/securedrop,jrosco/securedrop,pwplus/securedrop,heartsucker/securedrop,jrosco/securedrop,micahflee/securedrop