Fix many png warnings

...newview/skins/default/textures/icons/Conv_toolbar_pay.png

...ew/skins/default/textures/icons/Icon_Attachment_Large.png

...ew/skins/default/textures/icons/Icon_Attachment_Small.png

indra/newview/skins/default/textures/icons/MusicNote.png

indra/newview/skins/default/textures/icons/add_icon.png

...a/newview/skins/default/textures/icons/copy_clipboard.png

indra/newview/skins/default/textures/icons/delete_icon.png

indra/newview/skins/default/textures/icons/file_upload.png

...ewview/skins/default/textures/icons/multi_folder_mode.png

.../newview/skins/default/textures/icons/paste_clipboard.png

...wview/skins/default/textures/icons/profile_badge_beta.png

...ns/default/textures/icons/profile_badge_beta_lifetime.png

...w/skins/default/textures/icons/profile_badge_lifetime.png

...iew/skins/default/textures/icons/profile_badge_linden.png

...s/default/textures/icons/profile_badge_pplus_lifetime.png

...default/textures/icons/profile_badge_premium_lifetime.png

indra/newview/skins/default/textures/icons/remove_icon.png

...wview/skins/default/textures/icons/single_folder_back.png

...ew/skins/default/textures/icons/single_folder_forward.png

...wview/skins/default/textures/icons/single_folder_mode.png