find-dialog: find previous button and initial position next to the editor * file-editor-tab.cc(find): pass file editor to the find dialog * find-dialog.cc(constructor): new button for find previous, place dialog next to the editor (find_next,find_prev): new functions determining the search direction (find): renamed old function search_next, now with parameter for the dearch direction (replace_all): call function find instead of search next, message box with replaced items (no_matches_message): new function for message box on no more matches * find-dialog.h: new functions find, find_next, find_prev, no_matches_message, new button for find_prev